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diff --git a/37589.txt b/37589.txt new file mode 100644 index 0000000..b3046d1 --- /dev/null +++ b/37589.txt @@ -0,0 +1,7333 @@ +The Project Gutenberg eBook, Through Magic Glasses and Other Lectures, by +Arabella B. Buckley + + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + + + + +Title: Through Magic Glasses and Other Lectures + A Sequel to The Fairyland of Science + + +Author: Arabella B. Buckley + + + +Release Date: October 1, 2011 [eBook #37589] + +Language: English + +Character set encoding: ISO-646-US (US-ASCII) + + +***START OF THE PROJECT GUTENBERG EBOOK THROUGH MAGIC GLASSES AND OTHER +LECTURES*** + + +E-text prepared by Chris Curnow, Robin Shaw, and the Online Distributed +Proofreading Team (http://www.pgdp.net) from page images generously made +available by Internet Archive (http://www.archive.org) + + + +Note: Project Gutenberg also has an HTML version of this + file which includes the original illustrations. + See 37589-h.htm or 37589-h.zip: + (http://www.gutenberg.org/files/37589/37589-h/37589-h.htm) + or + (http://www.gutenberg.org/files/37589/37589-h.zip) + + + Images of the original pages are available through + Internet Archive. See + http://www.archive.org/details/throughmagicglas00buck + + + + + +[Illustration: For Description see Page 152 Frontispiece + +THE GREAT NEBULA OF ORION + +From a photograph taken on February 4th, 1889 by Mr Isaac Roberts.] + + +THROUGH MAGIC GLASSES AND OTHER LECTURES + +A Sequel to The Fairyland of Science + +by + +ARABELLA B. BUCKLEY +(Mrs. Fisher) + +Author of Life and Her Children, Winners in Life's Race, +A Short History of Natural Science, Etc. + +With Numerous Illustrations + + + + + + + +New York +D. Appleton and Company +1890 + +Authorized Edition. + + + + +PREFACE. + + +The present volume is chiefly intended for those of my young friends who +have read, and been interested in, the _Fairyland of Science_. It +travels over a wide field, pointing out a few of the marvellous facts +which can be studied and enjoyed by the help of optical instruments. It +will be seen at a glance that any one of the subjects dealt with might +be made the study of a lifetime, and that the little information given +in each lecture is only enough to make the reader long for more. + +In these days, when moderate-priced instruments and good books and +lectures are so easily accessible, I hope some eager minds may be thus +led to take up one of the branches of science opened out to us by magic +glasses; while those who go no further will at least understand +something of the hitherto unseen world which is now being studied by +their help. + +The two last lectures wander away from this path, and yet form a natural +conclusion to the Magician's lectures to his young Devonshire lads. They +have been published before, one in the _Youth's Companion_ of Boston, +U.S., and the other in _Atalanta_, in which the essay on Fungi also +appeared in a shorter form. All three lectures have, however, been +revised and fully illustrated, and I trust that the volume, as a whole, +may prove a pleasant Christmas companion. + +For the magnificent photograph of Orion's nebula, forming the +Frontispiece, I am indebted to the courtesy of Mr. Isaac Roberts, +F.R.A.S., who most kindly lent me the plate for reproduction; and I have +had the great good fortune to obtain permission from MM. Henri of the +Paris Observatory to copy the illustration of the Lunar Apennines from a +most beautiful and perfect photograph of part of the moon, taken by them +only last March. My cordial thanks are also due to Mr. A. Cottam, +F.R.A.S., for preparing the plate of coloured double stars, and to my +friend Mr. Knobel, Hon. Sec. of the R.A.S., for much valuable +assistance; to Mr. James Geikie for the loan of some illustrations from +his _Geology_; and to Messrs. Longman for permission to copy Herschel's +fine drawing of Copernicus. + +With the exception of these illustrations and a few others, three of +which were kindly given me by Messrs. Macmillan, all the woodcuts have +been drawn and executed under the superintendence of Mr. Carreras, jun., +who has made my task easier by the skill and patience he has exercised +under the difficulties incidental to receiving instructions from a +distance. + + ARABELLA B. BUCKLEY. + +UPCOTT AVENEL, _Oct. 1890_. + + + + +TABLE OF CONTENTS + + + CHAPTER I PAGE + THE MAGICIAN'S CHAMBER BY MOONLIGHT 1 + + CHAPTER II + MAGIC GLASSES AND HOW TO USE THEM 27 + + CHAPTER III + FAIRY RINGS AND HOW THEY ARE MADE 55 + + CHAPTER IV + THE LIFE-HISTORY OF LICHENS AND MOSSES 75 + + CHAPTER V + THE HISTORY OF A LAVA STREAM 96 + + CHAPTER VI + AN HOUR WITH THE SUN 117 + + CHAPTER VII + AN EVENING AMONG THE STARS 145 + + CHAPTER VIII + LITTLE BEINGS FROM A MINIATURE OCEAN 172 + + CHAPTER IX + THE DARTMOOR PONIES 195 + + CHAPTER X + THE MAGICIAN'S DREAM OF ANCIENT DAYS 209 + + + + +LIST OF ILLUSTRATIONS + + + PLATES + + PHOTOGRAPH OF THE NEBULA OF ORION _Frontispiece_ + + TABLE OF COLOURED SPECTRA Plate I. _facing p._ 127 + + COLOURED DOUBLE STARS Plate II. _facing p._ 167 + + + WOODCUTS IN THE TEXT PAGE + + PARTIAL ECLIPSE OF THE MOON _Initial letter_ 1 + + A BOY ILLUSTRATING THE PHASES OF THE MOON 6 + + COURSE OF THE MOON IN THE HEAVENS 8 + + CHART OF THE MOON 10 + + FACE OF THE FULL MOON 11 + + TYCHO AND HIS SURROUNDINGS (from a photograph by De la Rue) 13 + + PLAN OF THE PEAK OF TENERIFFE 15 + + THE CRATER COPERNICUS 17 + + THE LUNAR APPENNINES (from a photograph by M.M. Henri) 19 + + THE CRATER PLATO SEEN SOON AFTER SUNRISE 20 + + DIAGRAM OF TOTAL ECLIPSE OF THE MOON 23 + + BOY AND MICROSCOPE _Initial letter_ 27 + + EYE-BALL SEEN FROM THE FRONT 30 + + SECTION OF AN EYE LOOKING AT A PENCIL 31 + + IMAGE OF A CANDLE-FLAME THROWN ON PAPER BY A LENS 33 + + ARROW MAGNIFIED BY A CONVEX LENS 35 + + STUDENT'S MICROSCOPE 36 + + SKELETON OF A MICROSCOPE 37 + + FOSSIL DIATOMS SEEN UNDER THE MICROSCOPE 39 + + AN ASTRONOMICAL TELESCOPE 41 + + TWO SKELETONS OF TELESCOPES 44 + + THE PHOTOGRAPHIC CAMERA 47 + + KIRCHHOFF'S SPECTROSCOPE 51 + + PASSAGE OF RAYS THROUGH THE SPECTROSCOPE 52 + + A GROUP OF FAIRY-RING MUSHROOMS _Initial letter_ 55 + + THREE FORMS OF VEGETABLE MOULD MAGNIFIED 61 + + _MUCOR MUCEDO_ GREATLY MAGNIFIED 63 + + YEAST CELLS GROWING UNDER THE MICROSCOPE 65 + + EARLY STAGES OF THE MUSHROOM 67 + + LATER STAGES OF THE MUSHROOM 68 + + MICROSCOPIC STRUCTURE OF MUSHROOM GILLS 69 + + A GROUP OF CUP LICHENS _Initial letter_ 75 + + EXAMPLES OF LICHENS FROM LIFE 77 + + SINGE-CELLED PLANTS GROWING 78 + + SECTIONS OF LICHENS 81 + + FRUCTIFICATION OF A LICHEN 83 + + A STEM OF FEATHERY MOSS FROM LIFE 85 + + MOSS-LEAF MAGNIFIED 87 + + _POLYTRICHUM COMMUNE_, A LARGE HAIR-MOSS 88 + + FRUCTIFICATION OF A MOSS 89 + + SPHAGNUM MOSS FROM A DEVONSHIRE BOG 93 + + SURFACE OF A LAVA-FLOW _Initial letter_ 96 + + VESUVIUS AS SEEN IN ERUPTION 97 + + TOP OF VESUVIUS IN 1864 100 + + DIAGRAMMATIC SECTION OF AN ACTIVE VOLCANO 105 + + SECTION OF A LAVA-FLOW 108 + + VOLCANIC GLASS WITH CRYSTALLITES AND MICROLITHS 109 + + VOLCANIC GLASS WITH WELL-DEVELOPED MICROLITHS 110 + + A PIECE OF DARTMOOR GRANITE 112 + + VOLCANIC GLASS SHOWING LARGE INCLUDED CRYSTALS 115 + + A TOTAL ECLIPSE OF THE SUN _Initial letter_ 117 + + FACE OF THE SUN PROJECTED ON A PIECE OF CARDBOARD 120 + + PHOTOGRAPH OF THE SUN'S FACE, taken by Mr. Selwyn + (Secchi, _Le Soleil_) 122 + + TOTAL ECLIPSE OF THE SUN, SHOWING CORONA AND PROMINENCES + (Guillemin, _Le Ciel_) 124 + + KIRCHHOFF'S EXPERIMENT ON THE DARK SODIUM LINE 128 + + THE SPECTROSCOPE ATTACHED TO THE TELESCOPE FOR SOLAR WORK 132 + + SUN-SPECTRUM AND PROMINENCE SPECTRUM COMPARED 134 + + RED PROMINENCES, as drawn by Mr. Lockyer 1869 136 + + A QUIET SUN-SPOT 140 + + A TUMULTUOUS SUN-SPOT 141 + + A STAR-CLUSTER _Initial letter_ 145 + + SOME CONSTELLATIONS SEEN ON LOOKING SOUTH IN MARCH FROM + SIX TO NINE O'CLOCK 148 + + THE CHIEF STARS OF ORION, WITH ALDEBARAN 149 + + THE TRAPEZIUM [Greek: th] ORIONIS 150 + + SPECTRUM OF ORION'S NEBULA AND SUN-SPECTRUM COMPARED 151 + + SOME CONSTELLATIONS SEEN ON LOOKING NORTH IN MARCH FROM + SIX TO NINE O'CLOCK 156 + + THE GREAT BEAR, SHOWING POSITION OF THE BINARY STAR 157 + + DRIFTING OF THE SEVEN STARS OF CHARLES'S WAIN 159 + + CASSIOPEIA AND THE HEAVENLY BODIES NEAR 162 + + [Greek: e] LYRAE, A DOUBLE-BINARY STAR 166 + + A SEASIDE POOL _Initial letter_ 172 + + A GROUP OF SEAWEEDS (natural size) 175 + + _ULVA LACTUCA_, a piece greatly magnified 176 + + SEAWEEDS, magnified to show fruits 177 + + A CORALLINE AND SERTULARIAN COMPARED 179 + + _SERTULARIA TENELLA_ HANGING IN WATER 180 + + _THURICOLLA FOLLICULATA_ AND _CHILOMONAS AMYGDALUM_ 182 + + A GROUP OF LIVING DIATOMS 184 + + A DIATOM GROWING 185 + + _CYDIPPE PILEUS_, ANIMAL AND STRUCTURE 187 + + THE SEA-MAT, _FLUSTRA FOLIACEA_ 191 + + DIAGRAM OF THE FLUSTRA ANIMAL 192 + + DARTMOOR PONIES _Initial letter_ 195 + + _EQUUS HEMIONUS_, THE HORSE-ASS OF TARTARY AND TIBET 201 + + PRZEVALSKY'S WILD HORSE 202 + + SKELETON OF AN ANIMAL OF THE HORSE-TRIBE 206 + + PALAEOLITHIC MAN CHIPPING FLINT TOOLS _Initial letter_ 209 + + SCENE IN PALAEOLITHIC TIMES 212 + + PALAEOLITHIC RELICS--NEEDLE, TOOTH, IMPLEMENT 213 + + MAMMOTH ENGRAVED ON IVORY 216 + + NEOLITHIC IMPLEMENTS--HATCHET, CELT, SPINDLE WHORL 219 + + A BURIAL IN NEOLITHIC TIMES 221 + + BRITISH RELICS--COIN, BRONZE CELT, AND BRACELET 223 + + BRITONS TAKING REFUGE IN THE CAVE 224 + + + + +THROUGH MAGIC GLASSES + + + + +CHAPTER I + +THE MAGICIAN'S CHAMBER BY MOONLIGHT + + +[Illustration] + +The full moon was shining in all its splendour one lovely August night, +as the magician sat in his turret chamber bathed in her pure white +beams, which streamed upon him through the open shutter in the wooden +dome above. It is true a faint gleam of warmer light shone from below +through the open door, for this room was but an offshoot at the top of +the building, and on looking down the turret stairs a lecture-room might +be seen below where a bright light was burning. Very little, however, of +this warm glow reached the magician, and the implements of his art +around him looked like weird gaunt skeletons as they cast their long +shadows across the floor in the moonlight. + +The small observatory, for such it was, was a circular building with +four windows in the walls, and roofed with a wooden dome, so made that +it could be shifted round and round by pulling certain cords. One +section of this dome was a shutter, which now stood open, and the strip, +thus laid bare to the night, was so turned as to face that part of the +sky along which the moon was moving. In the centre of the room, with its +long tube directed towards the opening, stood the largest magic glass, +the TELESCOPE, and in the dead stillness of the night, could be heard +distinctly the tick-tick of the clockwork, which kept the instrument +pointing to the face of the moon, while the room, and all in it, was +being carried slowly and steadily onwards by the earth's rotation on its +axis. It was only a moderate-sized instrument, about six feet long, +mounted on a solid iron pillar firmly fixed to the floor and fitted with +the clockwork, the sound of which we have mentioned; yet it looked like +a giant as the pale moonlight threw its huge shadow on the wall behind +and the roof above. + +Far away from this instrument in one of the windows, all of which were +now closed with shutters, another instrument was dimly visible. This was +a round iron table, with clawed feet, and upon it, fastened by screws, +were three tubes, so arranged that they all pointed towards the centre +of the table, where six glass prisms were arranged in a semicircle, each +one fixed on a small brass tripod. A strange uncanny-looking instrument +this, especially as the prisms caught the edge of the glow streaming up +the turret stair, and shot forth faint beams of coloured light on the +table below them. Yet the magician's pupils thought it still more +uncanny and mysterious when their master used it to read the alphabet of +light, and to discover by vivid lines even the faintest trace of a metal +otherwise invisible to mortal eye. + +For this instrument was the SPECTROSCOPE, by which he could break up +rays of light and make them tell him from what substances they came. +Lying around it were other curious prisms mounted in metal rims and +fitted with tubes and many strange devices, not to be understood by the +uninitiated, but magical in their effect when fixed on to the telescope +and used to break up the light of distant stars and nebulae. + +Compared with these mysterious glasses the PHOTOGRAPHIC CAMERA, standing +in the background, with its tall black covering cloth, like a hooded +monk, looked comparatively natural and familiar, yet it, too, had +puzzling plates and apparatus on the table near it, which could be +fitted on to the telescope, so that by their means pictures might be +taken even in the dark night, and stars, invisible with the strongest +lens, might be forced to write their own story, and leave their image on +the plate for after study. + +All these instruments told of the magician's power in unveiling the +secrets of distant space and exploring realms unknown, but in another +window, now almost hidden in the shadow, stood a fourth and +highly-prized helpmate, which belonged in one sense more to our earth, +since everything examined by it had to be brought near, and lie close +under its magnifying-glass. Yet the MICROSCOPE too could carry its +master into an unseen world, hidden to mortal eye by minuteness instead +of by distance. If in the stillness of night the telescope was his most +cherished servant and familiar friend, the microscope by day opened out +to him the fairyland of nature. + +As he sat on his high pedestal stool on this summer night with the +moonlight full upon him, his whole attention was centred on the +telescope, and his mind was far away from that turret-room, wandering +into the distant space brought so near to him; for he was waiting to +watch an event which brought some new interest every time it took +place--a total eclipse of the moon. To-night he looked forward to it +eagerly, for it happened that, just as the moon would pass into the +shadow of our earth, it would also cross directly in front of a star, +causing what is known as an "occultation" of the star, which would +disappear suddenly behind the rim of the dark moon, and after a short +time flash out on the other side as the satellite went on its way. + +How he wished as he sat there that he could have shown this sight to all +the eager lads whom he was teaching to handle and love his magic +glasses. For this magician was not only a student himself, he was a rich +man and the Founder and Principal of a large public school for boys of +the artisan class. He had erected a well-planned and handsome building +in the midst of the open country, and received there, on terms within +the means of their parents, working-lads from all parts of England, who, +besides the usual book-learning, received a good technical education in +all its branches. And, while he left to other masters the regular +school lessons, he kept for himself the intense pleasure of opening the +minds of these lads to the wonders of God's universe around them. + +You had only to pass down the turret stairs, into the large science +class-room below, to see at once that a loving hand and heart had +furnished it. Not only was there every implement necessary for +scientific work, but numerous rough diagrams covering the walls showed +that labour as well as money had been spent in decorating them. It was a +large oblong room, with four windows to the north, and four to the +south, in each of which stood a microscope with all the tubes, needles, +forceps, knives, etc., necessary for dissecting and preparing objects; +and between the windows were open shelves, on which were ranged +chemicals of various kinds, besides many strange-looking objects in +bottles, which would have amused a trained naturalist, for the lads +collected and preserved whatever took their fancy. + +On some of the tables were photographic plates laid ready for printing +off; on others might be seen drawings of the spectrum, made from the +small spectroscope fixed at one end of the room; on others lay small +direct spectroscopes which the lads could use for themselves. But +nowhere was a telescope to be seen. This was not because there were +none, for each table had its small hand-telescope, cheap but good. The +truth is that each of these instruments had been spirited away into the +dormitories that night, and many heads were lying awake on their +pillows, listening for the strike of the clock to spring out and see +the eclipse begin. + +[Illustration: Fig. 1. + +A boy illustrating the phases of the moon.] + +A mere glance round the room showed that the moon had been much studied +lately. On the black-board was drawn a rough diagram, showing how a boy +can illustrate for himself the moon's journey round the earth, by taking +a ball and holding it a little above his head at arm's length, while he +turns slowly round on his heel in a darkened room before a lighted lamp, +or better still before the lens of a magic lantern (Fig. 1). The lamp or +lens then represents the sun, the ball is the moon, the boy's head is +the earth. Beginning with the ball between him and the source of light, +but either a little above, or a little below the direct line between his +eye and it, he will see only the dark side of the ball, and the moon +will be on the point of being "new." Then as he turns slowly, a thin +crescent of light will creep over the side nearest the sun, and by +degrees encroach more and more, so that when he has turned through one +quarter of the round half the disc will be light. When he has turned +another quarter, and has his back to the sun, a full moon will face him. +Then as he turns on through the third quarter a crescent of darkness +creeps slowly over the side away from the sun, and gradually the bright +disc is eaten away by shadow till at the end of the third quarter half +the disc again only is light; then, when he has turned through another +quarter and completed the circle, he faces the light again and has a +dark moon before him. But he must take care to keep the moon a little +above or a little below his eye at new and full moon. If he brings it +exactly on a line with himself and the light at new moon, he will shut +off the light from himself and see the dark body of the ball against the +light, causing an _eclipse_ of the sun; while if he does the same at +full moon his head will cast a shadow on the ball causing an _eclipse_ +of the moon. + +There were other diagrams showing how and why such eclipses do really +happen at different times in the moon's path round the earth; but +perhaps the most interesting of all was one he had made to explain what +so few people understand, namely, that though the moon describes a +complete circle round our earth every month, yet she does not describe a +circle in space, but a wavy line inwards and outwards across the +earth's path round the sun. This is because the earth is moving on all +the while, carrying the moon with it, and it is only by seeing it drawn +before our eyes that we can realise how it happens. + +Thus suppose, in order to make the dates as simple as possible, that +there is a new moon on the 1st of some month. Then by the 9th (or +roughly speaking in 7-3/4 days) the moon will have described a quarter +of a circle round the earth as shown by the dotted line (Fig. 2), which +marks her position night after night with regard to us. Yet because she +is carried onwards all the while by the earth, she will really have +passed along the interrupted line - - - - between us and the sun. During +the next week her quarter of a circle will carry her round behind the +earth, so that we see her on the 17th as a full moon, yet her actual +movement has been onwards along the interrupted line on the farther side +of the earth. During the third week she creeps round another quarter of +a circle so as to be in advance of the earth on its yearly journey round +the sun, and reaches the end of her third quarter on the 24th. In her +last quarter she gradually passes again between the earth and the sun; +and though, as regards the earth, she appears to be going back round to +the same place where she was at the beginning of the month, and on the +31st is again a dark new moon, yet she has travelled onwards exactly as +much as we have, and therefore has really not described a circle in the +_heavens_ but a wavy line. + +[Illustration: Fig. 2. + +Diagram showing the moon's course during one month. The moon and the +earth are both moving onwards in the direction of the arrows. The earth +moves along the dark line, the moon along the interrupted line - - - -. +The dotted curved line .... shows the circle gradually described by the +moon round the earth as they move onwards.] + +Near to this last diagram hung another, well loved by the lads, for it +was a large map of the _face_ of the moon, that is of the side which is +_always_ turned towards us, because the moon turns once on her axis +during the month that she is travelling round the earth. On this map +were marked all the different craters, mountains, plains and shining +streaks which appear on the moon's face; while round the chart were +pictures of some of these at sunrise and sunset on the moon, or during +the long day of nearly a fortnight which each part of the face enjoys in +its turn. + +[Illustration: Fig. 3. + +Chart of the moon. + +Craters-- + + 1 Tycho. 4 Aristarchus. 7 Plato. 10 Petavius. + 2 Copernicus. 5 Eratosthenes. 8 Eudoxus. 11 Ptolemy. + 3 Kepler. 6 Archimedes. 9 Aristotle. + +Grey plains formerly believed to be seas-- + + A Mare Crisium. O Mare Imbrium. + C ---- Frigoris. Q Oceanus Procellarum. + G ---- Tranquillitatis. X Mare Foecunditatis. + H ---- Serenitatis. T ---- Humorum.] + +By studying this map, and the pictures, they were able, even in their +small telescopes, to recognise Tycho and Copernicus, and the mountains +of the moon, after they had once grown accustomed to the strange +changes in their appearance which take place as daylight or darkness +creeps over them. They could not however pick out more than some of the +chief points. Only the magician himself knew every crater and ridge +under all its varying lights, and now, as he waited for the eclipse to +begin, he turned to a lad who stood behind him, almost hidden in the +dark shadow--the one fortunate boy who had earned the right to share +this night's work. + +[Illustration: Fig. 3_a_. + +The full moon. (From Ball's _Starland_.)] + +"We have still half an hour, Alwyn," said he, "before the eclipse will +begin, and I can show you the moon's face well to-night. Take my place +here and look at her while I point out the chief features. See first, +there are the grey plains (A, C, G, etc.) lying chiefly in the lower +half of the moon. You can often see these on a clear night with the +naked eye, but you must remember that then they appear more in the upper +part, because in the telescope we see the moon's face inverted or upside +down. + +"These plains were once thought to be oceans, but are now proved to be +dry flat regions situated at different levels on the moon, and much like +what deserts and prairies would appear on our earth if seen from the +same distance. Looking through the telescope, is it not difficult to +imagine how people could ever have pictured them as a man's face? But +not so difficult to understand how some ancient nations thought the moon +was a kind of mirror, in which our earth was reflected as in a +looking-glass, with its seas and rivers, mountains and valleys; for it +does look something like a distant earth, and as the light upon it is +really reflected from the sun it was very natural to compare it to a +looking-glass. + +"Next cast your eye over the hundreds of craters, some large, others +quite small, which cover the moon's face with pitted marks, like a man +with small-pox; while a few of the larger rings look like holes made in +a window-pane, where a stone has passed through, for brilliant shining +streaks radiate from them on all sides like the rays of a star, covering +a large part of the moon. Brightest of all these starred craters is +Tycho, which you will easily find near the top of the moon (I, Fig. 3), +for you have often seen it in the small telescope. How grand it looks +to-night in the full moon (Fig. 3_a_)! It is true you see all the +craters better when the moon is in her quarters, because the light falls +sideways upon them and the shadows are more sharply defined; yet even at +the full the bright ray of light on Tycho's rim marks out the huge +cavity, and you can even see faintly the magnificent terraces which run +round the cup within, one below the other." + +[Illustration: Fig. 4. + +Tycho and his surroundings. (From a photograph of the moon taken by Mr. +De la Rue, 1863.)] + +"This cavity measures fifty-four miles across, so that if it could be +moved down to our earth it would cover by far the largest part of +Devonshire, or that portion from Bideford on the north, to the sea on +the south, and from the borders of Cornwall on the east, to Exeter on +the west, and it is 17,000 feet or nearly three miles in depth. Even in +the brilliant light of the full moon this enormous cup is dark compared +to the bright rim, but it is much better seen in about the middle of the +second quarter, when the rising sun begins to light up one side while +the other is in black night. The drawing on the wall (Fig. 4), which is +taken from an actual photograph of the moon's face, shows Tycho at this +time surrounded by the numerous other craters which cover this part of +the moon. You may recognise him by the gleaming peak in the centre of +the cup, and by his bright rim which is so much more perfect than those +of his companions. The gleaming peak is the top of a steep cone or hill +rising up 6000 feet, or more than a mile from the base of the crater, so +that even the summit is about two miles below the rim. + +"There is one very interesting point in Tycho, however, which is seen at +its very best at full moon. Look outside the bright rim and you will see +that from the shadow which surrounds it there spring on all sides those +strange brilliant streaks (see Fig. 3_a_) which I spoke of just now. +There are others quite as bright, or even brighter, round other craters, +Copernicus (Fig. 6), Kepler, and Aristarchus, lower down on the +right-hand side of the moon; but these of Tycho are far the most widely +spread, covering almost all the top of the face. + +"What are these streaks? We do not know. During the second quarter of +the moon, when the sun is rising slowly upon Tycho, lighting up his +peak and showing the crater beautifully divided into a bright cup in the +curve to the right, while a dense shadow lies in the left hollow, these +streaks are only faint, and among the many craters around (see Fig. 4) +you might even have some difficulty at first in finding the well-known +giant. But as the sun rises higher and higher they begin to appear, and +go on increasing in brightness till they shine with that wonderfully +silvery light you see now in the full moon." + +[Illustration: Fig. 5. + +Plan of the Peak of Teneriffe, showing how it resembles a lunar crater. +(A. Geikie.)] + +"Here is a problem for you young astronomers to solve, as we learn more +and more how to use the telescope with all its new appliances." + +The crater itself is not so difficult to explain, for we have many like +it on our earth, only not nearly so large. In fact, we might almost say +that our earthly volcanoes differ from those in the moon only by their +smaller size and by forming _mountains_ with the crater or cup on the +top; while the lunar craters lie flat on the surface of the moon, the +hollow of the cup forming a depression below it. The peak of Teneriffe +(Fig. 5), which is a dormant volcano, is a good copy in miniature on our +earth of many craters on the moon. The large plain surrounded by a high +rocky wall, broken in places by lava streams, the smaller craters +nestling in the cup, and the high peak or central crater rising up far +above the others, are so like what we see on the moon that we cannot +doubt that the same causes have been at work in both cases, even though +the space enclosed in the rocky wall of Teneriffe measures only eight +miles across, while that of Tycho measures fifty-four. + +"But of the streaks we have no satisfactory explanation. They pass alike +over plain and valley and mountain, cutting even across other craters +without swerving from their course. The astronomer Nasmyth thought they +were the remains of cracks made when the volcanoes were active, and +filled with molten lava from below, as water oozes up through ice-cracks +on a pond. But this explanation is not quite satisfactory, for the lava, +forcing its way through, would cool in ridges which ought to cast a +shadow in sunlight. These streaks, however, not only cast no shadow, as +you can see at the full moon but when the sun shines sideways upon them +in the new or waning moon they disappear as we have seen altogether. +Thus the streaks, so brilliant at full moon in Tycho, Copernicus, +Kepler, and Aristarchus, remain a puzzle to astronomers still." + +[Illustration: Fig. 6. + +The crater Copernicus. (As given in Herschel's _Astronomy_, from a +drawing taken in a reflecting telescope of 20 feet focal length.)] + +"We cannot examine these three last-named craters well to-night with the +full sun upon them; but mark their positions well, for Copernicus, at +least, you must examine on the first opportunity, when the sun is +rising upon it in the moon's second quarter. It is larger even than +Tycho, measuring fifty-six miles across, and has a hill in the centre +with many peaks; while outside, great spurs or ridges stretch in all +directions sometimes for more than a hundred miles, and between these +are scattered innumerable minute craters. But the most striking feature +in it is the ring, which is composed inside the crater of magnificent +terraces divided by deep ravines. These terraces are in some ways very +like those of the great crater of Teneriffe, and astronomers can best +account for them by supposing that this immense crater was once filled +with a lake of molten lava rising, cooling at the edges, and then +falling again, leaving the solid ridge behind. The streaks are also +beautifully shown in Copernicus (see Fig. 6), but, as in Tycho, they +fade away as the sun sets on the crater, and only reappear gradually as +midday approaches. + +"And now, looking a little to the left of Copernicus, you will see that +grand range of mountains, the Lunar Apennines (Fig. 7), which stretches +400 miles across the face of the moon. Other mountain ranges we could +find, but none so like mountains on our own globe as these, with their +gentle sunny slope down to a plain on the left, and steep perpendicular +cliffs on the right. The highest peak in this range, called Huyghens, +rises to the height of 21,000 feet, higher than Chimborazo in the Andes. +Other mountains on the moon, such as those called the Caucasus, south of +the Apennines, are composed of disconnected peaks, while others again +stand as solitary pyramids upon the plains." + +[Illustration: Fig. 7. + +The Lunar Apennines. + +(Copied by kind permission of MM. Henri from part of a magnificent +photograph taken by them, March 29, 1890, at the Paris Observatory.)] + +"But we must hasten on, for I want you to observe those huge walled +crater-plains which have no hill in the middle, but smooth steel-grey +centres shining like mirrors in the moonlight. One of these, called +Archimedes, you will find just below the Lunar Apennines (Figs. 3 and +7), and another called Plato, which is sixty miles broad, is still lower +down the moon's face (Figs. 3 and 8). The centres of these broad +circles are curiously smooth and shining like quicksilver, with minute +dots here and there which are miniature craters, while the walls are +rugged and crowned with turret-shaped peaks." + +[Illustration: Fig. 8. + +The crater Plato as seen soon after sunrise. (After Neison.)] + +"It is easy to picture to oneself how these may once have been vast seas +of lava, not surging as in Copernicus, and heaving up as it cooled into +one great central cone, but seething as molten lead does in a crucible, +little bubbles bursting here and there into minute craters; and this is +the explanation given of them by astronomers. + +"And now that you have seen the curious rugged face of the moon and its +craters and mountains, you will want to know how all this has come +about. We can only form theories on the point, except that everything +shows that heat and volcanoes have in some way done the work, though no +one has ever yet clearly proved that volcanic eruptions have taken place +in our time. We must look back to ages long gone by for those mighty +volcanic eruptions which hurled out stones and ashes from the great +crater of Tycho, and formed the vast seas of lava in Copernicus and +Plato. + +"And when these were over, and the globe was cooling down rapidly, so +that mountain ranges were formed by the wrinkling and rending of the +surface, was there then any life on the moon? Who can tell? Our magic +glasses can reveal what now is, so far as distance will allow; but what +has been, except where the rugged traces remain, we shall probably never +know. What we now see is a dead worn-out planet, on which we cannot +certainly trace any activity except that of heat in the past. That there +is no life there now, at any rate of the kind on our own earth, we are +almost certain; first, because we can nowhere find traces of water, +clouds, nor even mist, and without moisture no life like ours is +possible; and secondly, because even if there is, as perhaps there may +be, a thin ocean of gas round the moon there is certainly no atmosphere +such as surrounds our globe. + +"One fact which proves this is, that there are no half-shadows on the +moon. If you look some night at the mountains and craters during her +first and second quarters, you will be startled to see what heavy +shadows they cast, not with faint edges dying away into light, but sharp +and hard (see Figs. 6-8), so that you pass, as it were by one step, from +shadow to sunshine. This in itself is enough to show that there is no +air to scatter the sunlight and spread it into the edges of the shade as +happens on our earth; but there are other and better proofs. One of +these is, that during an eclipse of the sun there is no reflection of +his light round the dark moon as there would be if the moon had an +atmosphere; another is that the spectroscope, that wonderful instrument +which shows us invisible gases, gives no hint of air around the moon; +and another is the sudden disappearance or _occultation_ of a star +behind the moon, such as I hope to see in a few minutes. + +"See here! take the small hand telescope and turn it on to the moon's +face while I take my place at the large one, and I will tell you what to +look for. You know that at sunset we see the sun for some time after it +has dipped below the horizon, because the rays of light which come from +it are bent in our atmosphere and brought to our eyes, forming in them +the image of the sun which is already gone. Now in a short time the moon +which we are watching will be darkened by our earth coming between it +and the sun, and while it is quite dark it will pass over a little +bright star. In fact to us the star will appear to set behind the dark +moon as the sun sets below the horizon, and if the moon had an +atmosphere like ours, the rays from the star would be bent in it and +reach our eyes after the star was gone, so that it would only disappear +gradually. Astronomers have always observed, however, that the star is +lost to sight quite suddenly, showing that there is no ocean of air +round the moon to bend the light-rays." + +[Illustration: Fig. 9. + +Diagram of total eclipse of the moon. + +S, Sun. E, Earth. M, Moon passing into the earth's shadow and passing +out at M'. + +R, R', Lines meeting at a point U, U' behind the earth and enclosing a +space within which all the direct rays of the sun are intercepted by the +earth, causing a black darkness or _umbra_. + +R, P and R', P', Lines marking a space within which, behind the earth, +part of the sun's rays are cut off, causing a half-shadow or _penumbra_, +P, P'. + +_a_, _a_, Points where a few of the sun's rays are bent or refracted in +the earth's atmosphere, so that they pass along the path marked by the +dotted lines and shed a lurid light on the sun's face.] + +Here the magician paused, for a slight dimness on the lower right-hand +side of the moon warned him that she was entering into the _penumbra_ or +half-shadow (see Fig. 9) caused by the earth cutting off part of the +sun's rays; and soon a deep black shadow creeping over Aristarchus and +Plato showed that she was passing into that darker space or _umbra_ +where the body of the earth is completely between her and the sun and +cuts off all his rays. All, did I say? No! not all. For now was seen a +beautiful sight, which would prove to any one who saw our earth from a +great distance that it has a deep ocean of air round it. + +It was a clear night, with a cloudless sky, and as the deep shadow crept +slowly over the moon's face, covering the Lunar Apennines and +Copernicus, and stealing gradually across the brilliant streaks of Tycho +till the crater itself was swallowed up in darkness, a strange lurid +light began to appear. The part of the moon which was eclipsed was not +wholly dark, but tinted with a very faint bluish-green light, which +changed almost imperceptibly, as the eclipse went on, to rose-red, and +then to a fiery copper-coloured glow as the moon crept entirely into the +shadow and became all dark. The lad watching through his small telescope +noted this weird light, and wondered, as he saw the outlines of the +Apennines and of several craters dimly visible by it, though the moon +was totally eclipsed. He noted, but was silent. He would not disturb the +Principal, for the important moment was at hand, as this dark +copper-coloured moon, now almost invisible, drew near to the star over +which it was to pass. + +This little star, really a glorious sun billions of miles away behind +the moon, was perhaps the centre of another system of worlds as unknown +to us as we to them, and the fact of our tiny moon crossing between it +and our earth would matter as little as if a grain of sand was blown +across the heavens. Yet to the watchers it was a great matter--would the +star give any further clue to the question of an atmosphere round the +moon? Would its light linger even for a moment, like the light of the +setting sun? Nearer and nearer came the dark moon; the star shone +brilliantly against its darkness; one second and it was gone. The long +looked-for moment had passed, and the magician turned from his +instrument with a sigh. "I have learnt nothing new, Alwyn," said he, +"but at least it is satisfactory to have seen for ourselves the proof +that there is no perceptible atmosphere round the moon. We need wait no +longer, for before the star reappears on the other side the eclipse will +be passing away." + +"But, master," burst forth the lad, now the silence was broken, "tell me +why did that strange light of many tints shine upon the dark moon?" + +"Did you notice it, Alwyn?" said the Principal, with a pleased smile. +"Then our evening's work is not lost, for you have made a real +observation for yourself. That light was caused by the few rays of the +sun which grazed the edge of our earth passing through the ocean of air +round it (see Fig. 9). There they were refracted or bent, and so were +thrown within the shadow cast by our earth, and fell upon the moon. If +there were such a person as a 'man in the moon,' that lurid light would +prove to him that our earth has an atmosphere. The cause of the tints is +the same which gives us our sunset colours, because as the different +coloured waves which make white light are absorbed one by one, passing +through the denser atmosphere, the blue are cut off first, then the +green, then the yellow, till only the orange and red rays reached the +centre of the shadow, where the moon was darkest. But this is too +difficult a subject to begin at midnight." + +So saying, he lighted his lamp, and covering the object-glass of his +telescope with its pasteboard cap, detached the instrument from the +clockwork, and the master and his pupil went down the turret stairs and +past through the room below. As they did so they heard in the distance a +scuffling noise like that of rats in the wall. A smile passed over the +face of the Principal, for he knew that his young pupils, who had been +making their observations in the gallery above, were hurrying back to +their beds. + + + + +CHAPTER II + +MAGIC GLASSES, AND HOW TO USE THEM + + +[Illustration] + +The sun shone brightly into the science class-room at mid-day. No gaunt +shadows nor ghostly moonlight now threw a spell on the magic chamber +above. The instruments looked bright and business-like, and the +Principal, moving amongst them, heard the subdued hum of fifty or more +voices rising from below. It was the lecture hour, and the subject for +the day was, "Magic glasses, and how to use them." As the large clock in +the hall sounded twelve, the Principal gathered up a few stray lenses +and prisms he had selected, and passed down the turret stair to his +platform. Behind him were arranged his diagrams, before him on the table +stood various instruments, and the rows of bright faces beyond looked up +with one consent as the hum quieted down and he began his lecture. + +"I have often told you, boys, have I not? that I am a Magician. In my +chamber near the sky I work spells as did the magicians of old, and by +the help of my magic glasses I peer into the secrets of nature. Thus I +read the secrets of the distant stars; I catch the light of wandering +comets, and make it reveal its origin; I penetrate into the whirlpools +of the sun; I map out the craters of the moon. Nor can the tiniest being +on earth hide itself from me. Where others see only a drop of muddy +water, that water brought into my magic chamber teems with thousands of +active bodies, darting here and whirling there amid a meadow of tiny +green plants floating in the water. Nay, my inquisitive glass sees even +farther than this, for with it I can watch the eddies of water and green +atoms going on in each of these tiny beings as they feed and grow. +Again, if I want to break into the secrets of the rock at my feet, I +have only to put a thin slice of it under my microscope to trace every +crystal and grain; or, if I wish to learn still more, I subject it to +fiery heat, and through the magic prisms of my spectroscope I read the +history of the very substances of which it is composed. If I wish to +study the treasures of the wide ocean, the slime from a rock-pool teems +with fairy forms darting about in the live box imprisoned in a crystal +home. If some distant stars are invisible even in the giant glasses of +my telescope, I set another power to work, and make them print their own +image on a photographic plate and so reveal their presence. + +"All these things you have seen through my magic glasses, and I +promised you that one day I would explain to you how they work and do my +bidding. But I must warn you that you must give all your attention; +there is no royal road to my magician's power. Every one can attain to +it, but only by taking trouble. You must open your eyes and ears, and +use your intelligence to test carefully what your senses show you. + +"We have only to consider a little to see that we depend entirely upon +our senses for our knowledge of the outside world. All kinds of things +are going on around us, about which we know nothing, because our eyes +are not keen enough to see, and our ears not sharp enough to hear them. +Most of all we enjoy and study nature through our eyes, those windows +which let in to us the light of heaven, and with it the lovely sights +and scenes of earth; and which are no ordinary windows, but most +wonderful structures adapted for conveying images to the brain. They are +of very different power in different people, so that a long-sighted +person sees a lovely landscape where a short-sighted one sees only a +confused mist; while a short-sighted person can see minute things close +to the eye better than a long-sighted one." + +[Illustration: Fig. 10. + +Eye-ball seen from the front. (After Le Gros Clark.) + +_w_, White of eye. _i_, Iris. _p_, Pupil.] + +"Let us try to understand this before we go on to artificial glasses, +for it will help us to explain how these glasses show us many things we +could never see without them. Here are two pictures of the human eyeball +(Figs. 10 and 11), one as it appears from the front, and the other as we +should see the parts if we cut an eyeball across from the front to the +back. From these drawings we see that the eyeball is round; it only +looks oval, because it is seen through the oval slit of the eyelids. +It is really a hard, shining, white ball with a thick nerve cord +(_on_, Fig. 11) passing out at the back, and a dark glassy mound +_c_, _c_ in the centre of the white in front. In this mound we can +easily distinguish two parts--first, the coloured _iris_ or elastic +curtain (_i_, Fig. 10); and secondly, the dark spot or pupil _p_ in the +centre. The iris is the part which gives the eye its colour; it is +composed of a number of fibres, the outer ones radiating towards the +centre, the inner ones forming a ring round the pupil; and behind these +fibres is a coat of dark pigment or colouring matter, blue in some +people, grey, brown, or black in others. When the light is very strong, +and would pain the nerves inside if too much entered the pupil or window +of the eye, then the ring of the iris contracts so as partly to close +the opening. When there is very little light, and it is necessary to let +in as much as possible, the ring expands and the pupil grows large. The +best way to observe this is to look at a cat's eyes in the dusk, and +then bring her near to a bright light; for the iris of a cat's eye +contracts and expands much more than ours does." + +[Illustration: Fig. 11. + +Section of an eye looking at a pencil. (Adapted from Kirke.) + +_c_, _c_, Cornea. _w_, White of eye. _cm_, Ciliary muscle. _a_, _a_, +Aqueous humour. _i_, _i_, Iris. _l_, _l_, Lens. _r_, _r_, Retina. _on_, +Optic nerve. 1, 2, Pencil. 1', 2', Image of pencil on the retina.] + +"Now look at the second diagram (Fig. 11) and notice the chief points +necessary in seeing. First you will observe that the pupil is not a mere +hole; it is protected by a curved covering _c_. This is the cornea, a +hard, perfectly transparent membrane, looking much like a curved +watch-glass. Behind this is a small chamber filled with a watery fluid +_a_, called the aqueous humour, and near the back of this chamber is the +dark ring or iris _i_, which you saw from the front through the cornea +and fluid. Close behind the iris again is the natural 'magic glass' of +our eye, the crystalline lens _l_, which is composed of perfectly +transparent fibres and has two rounded or convex surfaces like an +ordinary magnifying glass. This lens rests on a cushion of a soft +jelly-like substance _v_, called the vitreous humour, which fills the +dark chamber or cavity of the eyeball and keeps it in shape, so that the +retina _r_, which lines the chamber, is kept at a proper distance from +the lens. This retina is a transparent film of very sensitive nerves; it +forms a screen at the back of the chamber, and has a coating of very +dark pigment or colouring matter behind it. Lastly, the nerves of the +retina all meet in a bundle, called the optic nerve, and passing out of +the eyeball at a point _on_, go to the brain. These are the chief parts +we use in seeing; now how do we use them? + +"Suppose that a pencil is held in front of the eye at the distance at +which we see small objects comfortably. Light is reflected from all +parts of the surface of the pencil, and as the rays spread, a certain +number enter the pupil of the eye. We will follow only two cones of +light coming from the points 1 and 2 on the diagram Fig. 11. These you +see enter the eye, each widely spread over the cornea _c_. They are bent +in a little by this curved covering, and by the liquid behind it, while +the iris cuts off the rays near the edges of the lens, which would be +too much bent to form a clear image. The rest of the rays fall upon the +lens _l_. In passing through this lens they are very much bent (or +_refracted_) towards each other, so much so that by the time they reach +the end of the dark chamber _v_, each cone of light has come to a point +or focus 1', 2', and as rays of this kind have come from every point all +over the pencil, exactly similar points are formed on the retina, and a +real picture of the pencil is formed there between 1' and 2'." + +[Illustration: Fig. 12. + +Image of a candle-flame thrown on paper by a lens.] + +"We will make a very simple and pretty experiment to illustrate this. +Darkening the room I light a candle, take a square of white paper in my +hand, and hold a simple magnifying glass between the two (see Fig. 12) +about three inches away from the candle. Then I shift the paper nearer +and farther behind the lens, till we get a clear image of the +candle-flame upon it. This is exactly what happens in our eye. I have +drawn a dotted line _c_ round the lens and the paper on the diagram to +represent the eyeball in which the image of the candle-flame would be on +the retina instead of on the piece of paper. The first point you will +notice is that the candle-flame is upside down on the paper, and if you +turn back to Fig. 11 you will see why, for it is plain that the cones of +light _cross_ in the lens _l_, 1 going to 1' and 2 to 2'. Every picture +made on our retina is upside down. + +"But it is not there that we see it. As soon as the points of light from +the pencil strike upon the retina, the thrill passes on along the optic +nerve _on_, through the back of the eye to the brain; and our mind, +following back the rays exactly as they have come through the lens, sees +a pencil, outside the eye, right way upwards. + +"This is how we see with our eyes, which adjust themselves most +beautifully to our needs. For example, not only is the iris always ready +to expand or contract according as we need more or less light, but there +is a special muscle, called the ciliary muscle (_cm_, Fig. 11), which +alters the lens for us to see things far or near. In all, or nearly all, +perfect eyes the lens is flatter in front than behind, and this enables +us to see things far off by bringing the rays from them exactly to a +focus on the retina. But when we look at nearer things the rays require +to be more bent or refracted, so without any conscious effort on our +part this ciliary muscle contracts and allows the lens to bulge out +slightly in front. Instantly we have a stronger magnifier, and the rays +are brought to the right focus on the retina, so that a clear and +full-size image of the near object is formed. How little we think, as we +turn our eyes from one thing to another, and observe, now the distant +hills, now the sheep feeding close by; or, as night draws on, gaze into +limitless space and see the stars millions upon millions of miles away, +that at every moment the focus of our eye is altering, the iris is +contracting or expanding, and myriads of images are being formed one +after the other in that little dark chamber, through which pass all the +scenes of the outer world! + +"Yet even this wonderful eye cannot show us everything. Some see farther +than others, some see more minutely than others, according as the lens +of the eye is flatter in one person and more rounded in another. But the +most long-sighted person could never have discovered the planet Neptune, +more than 2700 millions of miles distant from us, nor could the +keenest-sighted have known of the existence of those minute and +beautiful little plants, called diatoms, which live around us wherever +water is found, and form delicate flint skeletons so infinitesimally +small that thousands of millions go to form one cubic inch of the stone +called tripoli, found at Bilin in Bohemia." + +[Illustration: Fig. 13. + +Arrow magnified by a convex lens. + +_a_, _b_, Real arrow. C, D, Magnifying-glass. A, B, Enlarged image of +the arrow.] + +"It is here that our 'magic glasses' come to our assistance, and reveal +to us what was before invisible. We learnt just now that we see near +things by the lens of our eye becoming more rounded in front; but there +comes a point beyond which the lens cannot bulge any more, so that when +a thing is very tiny, and would have to be held very close to the eye +for us to see it, the lens can no longer collect the rays to a focus, so +we see nothing but a blur. More than 800 years ago an Arabian, named +Alhazen, explained why rounded or convex glasses make things appear +larger when placed before the eye. This glass which I hold in my hand +is a simple magnifying-glass, such as we used for focusing the +candle-flame. It bends the rays inwards from any small object (see the +arrow _a_, _b_, Fig. 13) so that the lens of our eye can use them, and +then, as we follow out the rays in straight lines to the place where we +see clearly (at A, B), every point of the object is magnified, and we +not only see it much larger, but every mark upon it is much more +distinct. You all know how the little shilling magnifying-glasses you +carry show the most lovely and delicate structures in flowers, on the +wings of butterflies, on the head of a bee or fly, and, in fact, in all +minute living things." + +[Illustration: Fig. 14. + +Student's microscope. _ep_, Eye-piece. _o_, _g_, Object-glass.] + +[Illustration: Fig. 15. + +Skeleton of a microscope, showing how an object is magnified. + +_o_, _l_, Object-lens. _e_, _g_, Eye-glass. _s_, _s_, Spicule. +_s'_, _s'_, Magnified image of same in the tube. S, S, Image again +enlarged by the lens of the eye-piece.] + +"But this is only our first step. Those diatoms we spoke of just now +will only look like minute specks under even the strongest +magnifying-glass. So we pass on to use two extra lenses to assist our +eyes, and come to this compound microscope (Fig. 14) through which I +have before now shown you the delicate markings on shells which were +themselves so minute that you could not see them with the naked eye. Now +we have to discover how the microscope performs this feat. Going back +again for a minute to our candle and magnifying-glass (Fig. 12), you +will find that the nearer you put the lens to the candle the farther +away you will have to put the paper to get a clear image. When in a +microscope we put a powerful lens _o_, _l_ close down to a very minute +object, say a spicule of a flint sponge _s_, _s_, quite invisible to the +unaided eye, the rays from this spicule are brought to a focus a long +way behind it at _s'_, _s'_, making an enlarged image because the lines +of light have been diverging ever since they crossed in the lens. If you +could put a piece of paper at _s'_ _s'_, as you did in the candle +experiment, you would see the actual image of the magnified spicule upon +it. But as these points of light are only in an empty tube, they pass +on, spreading out again from the image, as they did before from the +spicule. Then another convex lens or eye-glass _e_, _g_ is put at the +top of the microscope at the proper distance to bend these rays so that +they enter our eye in nearly parallel lines, exactly as we saw in the +ordinary magnifying-glass (Fig. 13), and our crystalline lens can then +bring them to a focus on our retina. + +"By this time the spicule has been twice magnified; or, in other words, +the rays of light coming from it have been twice bent towards each +other, so that when our eye follows them out in straight lines they are +widely spread, and we see every point of light so clearly that all the +spots and markings on this minute spicule are as clear as if it were +really as large as it looks to us. + +"This is simply the principle of the microscope. When you come to look +at your own instruments, though they are very ordinary ones, you will +find that the object-glass _o_, _l_ is made of three lenses, flat on the +side nearest the tube, and each lens is composed of two kinds of glass +in order to correct the unequal refraction of the rays, and prevent +fringes of colour appearing at the edge of the lens. Then again the +eye-piece will be a short tube with a lens at each end, and halfway +between them a black ledge will be seen inside the tube which acts like +the iris of our eye (_i_, Fig. 11) and cuts off the rays passing through +the edges of the lens. All these are devices to correct faults in the +microscope which our eye corrects for itself, and they have enabled +opticians to make very powerful lenses. + +"Look now at the diagram (Fig. 16) showing a group of diatoms which you +can see under the microscope after the lecture. Notice the lovely +patterns, the delicate tracery, and the fine lines on the diatoms shown +there. Yet each of these minute flint skeletons, if laid on a piece of +glass by itself, would be quite invisible to the naked eye, while +hundreds of them together only look like a faint mist on the slide on +which they lie. Nor are they even here shown as much magnified as they +might be; under a stronger power we should see those delicate lines on +the diatoms broken up into minute round cups." + +[Illustration: Fig. 16. + +Fossil diatoms seen under the microscope. The largest of these is an +almost imperceptible speck to the naked eye.] + +"Is it not wonderful and delightful to think that we are able to add in +this way to the power of our eyes, till it seems as if there were no +limit to the hidden beauties of the minute forms of our earth, if only +we can discover them? + +"But our globe does not stand alone in the universe, and we want not +only to learn all about everything we find upon it, but also to look out +into the vast space around us and discover as much as we can about the +myriads of suns and planets, comets and meteorites, star-mists and +nebulae, which are to be found there. Even with the naked eye we can +admire the grand planet Saturn, which is more than 800 millions of miles +away, and this in itself is very marvellous. Who would have thought that +our tiny crystalline lens would be able to catch and focus rays, sent +all this enormous distance, so as actually to make a picture on our +retina of a planet, which, like the moon, is only sending back to us the +light of the sun? For, remember, the rays which come to us from Saturn +must have travelled twice 800 millions of miles--884 millions from the +sun to the planet, and less or more from the planet back to us, +according to our position at the time. But this is as nothing when +compared to the enormous distances over which light travels from the +stars to us. Even the nearest star we know of, is at least twenty +_millions_ of _millions_ of miles away, and the light from it, though +travelling at the rate of 186,300 miles in a second, takes four years +and four months to reach us, while the light from others, which we can +see without a telescope, is between twenty and thirty years on its road. +Does not the thought fill us with awe, that our little eye should be +able to span such vast distances? + +"But we are not yet nearly at the end of our wonder, for the same power +which devised our eye gave us also the mind capable of inventing an +instrument which increases the strength of that eye till we can actually +see stars so far off that their light takes _two thousand years_ coming +to our globe. If the microscope delights us in helping us to see things +invisible without it, because they are so small, surely the telescope is +fascinating beyond all other magic glasses when we think that it brings +heavenly bodies, thousands of billions of miles away, so close to us +that we can examine them." + +[Illustration: Fig. 17. + +An astronomical telescope. + +_ep_, Eye-piece. _og_, Object-glass. _f_, Finder.] + +"A Telescope (Fig. 17) can, like the microscope, be made of only two +glasses: an object-glass to form an image in the tube and a magnifying +eye-piece to enlarge it. But there is this difference, that the object +lens of a microscope is put close down to a minute object, so that the +rays fall upon it at a wide angle, and the image formed in the tube is +very much larger than the object outside. In the telescope, on the +contrary, the thing we look at is far off, so that the rays fall on the +object-glass at such a very narrow angle as to be practically parallel, +and the image in the tube is of course _very, very_ much smaller than +the house, or church, or planet it pictures. What the object-glass of +the telescope does for us, is to bring a small _real image_ of an object +very far off close to us in the tube of the telescope so that we can +examine it. + +"Think for a moment what this means. Imagine that star we spoke of (p. +41), whose light, travelling 186,300 miles in one second, still takes +2000 years to reach us. Picture the tiny waves of light crossing the +countless billions of miles of space during those two thousand years, +and reaching us so widely spread out that the few faint rays which +strike our eye are quite useless, and for us that star has no existence; +we cannot see it. Then go and ask the giant telescope, by turning the +object-glass in the direction where that star lies in infinite space. +The widespread rays are collected and come to a minute bright image in +the dark tube. You put the eye-piece to this image, and there, under +your eye, is a shining point: this is the image of the star, which +otherwise would be lost to you in the mighty distance. + +"Can any magic tale be more marvellous, or any thought grander, or more +sublime than this? From my little chamber, by making use of the laws of +light, which are the same wherever we turn, we can penetrate into depths +so vast that we are not able even to measure them, and bring back unseen +stars to tell us the secrets of the mighty universe. As far as the stars +are concerned, whether we see them or not depends entirely upon the +number of rays collected by the object-glass; for at such enormous +distances the rays have no angle that we can measure, and magnify as +you will, the brightest star only remains a point of light. It is in +order to collect enough rays that astronomers have tried to have larger +and larger object-glasses; so that while a small good hand telescope, +such as you use, may have an object-glass measuring only an inch and a +quarter across, some of the giant telescopes have lenses of two and a +half feet, or thirty inches, diameter. These enormous lenses are very +difficult to make and manage, and have many faults, therefore +astronomical telescopes are often made with curved mirrors to _reflect_ +the rays, and bring them to a focus instead of _refracting_ them as +curved lenses do. + +"We see, then, that one very important use of the telescope is to bring +objects into view which otherwise we would never see; for, as I have +already said, though we bring the stars into sight, we cannot magnify +them. But whenever an object is near enough for the rays to fall even at +a very small perceptible angle on the object-glass, then we can magnify +them; and the longer the telescope, and the stronger the eye-piece, the +more the object is magnified. + +[Illustration: Fig. 18. + +Skeletons of telescopes. + +A, A one-foot telescope with a three-inch eye-piece. B, A two-foot +telescope with a three-inch eye-piece. _e_, _p_, Eye-piece. _o_, _g_, +Object-glass. _r_, _r_, Rays which enter the telescopes and crossing at +_x_ form an image at _i_, _i_, which is magnified by the lens _e_, _p_. +The angles _r_, _x_, _r_ and _i_, _x_, _i_ are the same. In A the angle +_i_, _o_, _i_ is four times greater than that of _i_, _x_, _i_. In B it +is eight times greater.] + +"I want you to understand the meaning of this, for it is really very +simple, only it requires a little thought. Here are skeleton drawings of +two telescopes (Fig. 18), one double the length of the other. Let us +suppose that two people are using them to look at an arrow on a +weathercock a long distance off. The rays of light _r_, _r_ from the +two ends of the arrow will enter both telescopes at the same angle +_r_, _x_, _r_, cross in the lens, and pass on at _exactly the same +angle_ into the tubes. So far all is alike, but now comes the +difference. In the short telescope A the object-glass must be of such a +curve as to bring the cones of light in each ray to a focus at a +distance of _one foot_ behind it,[1] and there a small image _i_, _i_ of +the arrow is formed. But B being twice the length, allows the lens +to be less curved, and the image to be formed _two feet_ behind the +object-glass; and as the rays _r_, _r_ have been _diverging_ ever since +they crossed at _x_, the real image of the arrow formed at _i_, _i_ is +twice the size of the same image in A. Nevertheless, if you could put a +piece of paper at _i_, _i_ in both telescopes, and look through the +_object-glass_ (which you cannot actually do, because your head would +block out the rays), the arrow would appear the same size in both +telescopes, because one would be twice as far off from you as the other, +and the angle _i_, _x_, _i_ is the same in both." + + [1] In our Fig. 18 the distances are inches instead of feet, but the + proportions are the same. + +"But by going to the proper end of the telescope you can get quite near +the image, and can see and magnify it, if you put a strong lens to +collect the rays from it to a focus. This is the use of the eye-piece, +which in our diagram is placed at a quarter of a foot or three inches +from the image in both telescopes. Now that we are close to the images, +the divergence of the points _i_, _i_ makes a great difference. In the +small telescope, in which the image is only _one foot_ behind the +object-glass, the eye-piece being a quarter of a foot from it, is four +times nearer, so the angle _i_, _o_, _i_ is four times the angle +_i_, _x_, _i_, and the man looking through it sees the image magnified +_four times_. But in the longer telescope the image is _two feet_ behind +the lens, while the eye-piece is, as before, a quarter of a foot from +it. Thus the eyepiece is now eight times nearer, so the angle +_i_, _o_, _i_ is eight times the angle _i_, _x_, _i_, and the observer +sees the image magnified _eight times_. + +"In real telescopes, where the difference between the focal length of +the object-glass and that of the eye-glass can be made enormously +greater, the magnifying power is quite startling, only the object-glass +must be large, so as to collect enough rays to bear spreading widely. +Even in your small telescopes, with a focus of eighteen inches, and an +object-glass measuring one and a quarter inch across, we can put on a +quarter of an inch eye-piece, and so magnify seventy-two times; while in +my observatory telescope, eight feet or ninety-six inches long, an +eye-piece of half an inch magnifies 192 times, and I can put on a +1/8-inch eye-piece and magnify 768 times! And so we can go on +lengthening the focus of the object-glass and shortening the focus of +the eye-piece, till in Lord Rosse's gigantic fifty-six-foot telescope, +in which the image is fifty-four feet (648 inches) behind the +object-glass, an eye-piece one-eighth of an inch from the image +magnifies 5184 times! These giant telescopes, however, require an +enormous object-glass or mirror, for the points of light are so spread +out in making the large image that it is very faint unless an enormous +number of rays are collected. Lord Rosse's telescope has a reflecting +mirror measuring six feet across, and a man can walk upright in the +telescope tube. The most powerful telescope yet made is that at the Lick +Observatory, on Mount Hamilton, in California. It is fifty-six and a +half feet long, the object-lens measures thirty-six inches across. A +star seen through this telescope appears 2000 times as bright as when +seen with the naked eye. + +"You need not, however, wait for an opportunity to look through giant +telescopes, for my small student's telescope, only four feet long, which +we carry out on to the lawn, will show you endless unseen wonders; while +your hand telescopes, and even a common opera-glass, will show many +features on the face of the moon, and enable you to see the crescent of +Venus, Jupiter's moons, and Saturn's rings, besides hundreds of stars +unseen by the naked eye. + +"Of course you will understand that Fig. 18 only shows the _principle_ +of the telescope. In all good instruments the lenses and other parts are +more complicated; and in a terrestrial telescope, for looking at +objects on the earth, another lens has to be put in to turn them right +way up again. In looking at the sky it does not matter which way up we +see a planet or a star, so the second glass is not needed, and we lose +light by using it. + +"We have now three magic glasses to work for us--the magnifying-glass, +the microscope, and the telescope. Besides these, however, we have two +other helpers, if possible even more wonderful. These are the +Photographic camera and the Spectroscope." + +[Illustration: Fig. 19. + +Photographic camera. + +_l_, _l_, Lenses. _s_, _s_, Screen cutting off diverging rays. _c_, _c_, +Sliding box. _p_, _p_, Picture formed.] + +"Now that we thoroughly understand the use of lenses, I need scarcely +explain this photographic camera (Fig. 19), for it is clearly an +artificial eye. In place of the _crystalline lens_ (compare with Fig. +11) the photographer uses one, or generally two lenses _l_, _l_, with a +black ledge or stop _s_ between them, which acts like the iris in +cutting off the rays too near the edge of the lens. The dark camera _c_ +answers to the _dark chamber_ of the eyeball, and the plate _p_, _p_ at +the back of the chamber, which is made sensitive by chemicals, answers +our _retina_. The box is formed of two parts, sliding one within the +other at _c_, so as to place the plate at a proper distance from the +lens, and then a screw adjusts the focus more exactly by bringing the +front lens back or forward, instead of altering the curve as the +_ciliary muscle_ does in our eye. The difference between the two +instruments is that in our eye the message goes to the brain, and the +image disappears when we turn our eyes away from the object; but in the +camera the waves of light work upon the chemicals, and the image can be +fixed and remain for ever. + +"But the camera has at least one weak point. The screen at the back is +not curved like our retina, but must be flat because of printing off the +pictures, and therefore the parts of the photograph near the edge are a +little out of proportion. + +"In many ways, however, this photographic eye is a more faithful +observer than our own, and helps us to make more accurate pictures. For +instance, instantaneous photographs have been taken of a galloping +horse, and we find that the movements are very different from what we +thought we saw with our eye, because our retina does not throw off one +impression after another quickly enough to be quite certain we see each +curve truly in succession. Again, the photograph of a face gives minute +curves and lines, lights and shadows, far more perfectly than even the +best artist can see them, and when the picture is magnified we see more +and more details which escaped us before. + +"But it is especially when attached to the microscope or the telescope +that the photographic apparatus tells us such marvellous secrets; +giving us, for instance, an accurate picture of the most minute +water-animal quite invisible to the naked eye, so that when we enlarge +the photograph any one can see the beautiful markings, the finest fibre, +or the tiniest granule; or affording us accurate pictures, such as the +one at p. 19 of the face of the moon, and bringing stars into view which +we cannot otherwise see even with the strongest telescope. + +"Our own eye has many weaknesses. For example, when we look through the +telescope at the sky we can only fix our attention on one part at once, +and afterwards on another; and the picture which we see in this way, bit +by bit, we must draw as best we can. But if we put a sensitive +photographic plate into the telescope just at the point (_i_, _i_, Fig. +18), where the _image_ of the sky is focused, this plate gives +attention, so to speak, to the whole picture at once, and registers +every point exactly as it is; and this picture can be kept and enlarged +so that every detail can be seen. + +"Then, again, if we look at faint stars, they do not grow any brighter +as we look. Each ray sends its message to the brain, and that is all; we +cannot heap them up in our eye, and, indeed, after a time we see less, +because our nerves grow tired. But on a photographic plate in a +telescope, each ray in its turn does a little work upon the chemicals, +and the longer the plate remains, the stronger the picture becomes. When +wet plates were used they could not be left long, but since dry plates +have been invented, with a film of chemically prepared gelatine, they +can be left for hours in the telescope, which is kept by clockwork +accurately opposite to the same objects. In this way thousands of faint +stars, which we cannot see with the strongest telescope, creep into view +as their feeble rays work over and over again on the same spot; and, as +the brighter stars as well as the faint ones are all the time making +their impression stronger, when the plate comes out each one appears in +its proper strength. On the other hand, very bright objects often become +blurred by a long exposure, so that we have sometimes to sacrifice the +clearness of a bright object in order to print faint objects clearly. + +"We now come to our last magic glass--the Spectroscope; and the hour has +slipped by so fast that I have very little time left to speak of it. But +this matters less as we have studied it before.[1] I need now only +remind you of some of the facts. You will remember that when we passed +sunlight through a three-sided piece of glass called a prism, we broke +up a ray of white light into a line of beautiful colours gradually +passing from red, through orange, yellow, green, blue, and indigo, to +violet, and that these follow in the same order as we see them in the +rainbow or in the thin film of a soap-bubble. By various experiments we +proved that these colours are separated from each other because the many +waves which make up white light are of different sizes, so that because +the waves, of red light are slow and heavy, they lag behind when bent in +the three-sided glass, while the rapid violet waves are bent more out of +their road and run to the farther end of the line, the other colours +ranging themselves between." + + [1] _Fairyland of Science_, Lecture II.; and _Short History of Natural + Science_, chapter xxxiv. + +"Now when the light falls through the open window, or through a round +hole or _large_ slit, the images of the hole made by each coloured wave +overlap each other very much, and the colours in the spectrum or +coloured band are crowded together. But when in the spectroscope we pass +the ray of light through a very narrow slit, each coloured image of the +upright slit overlaps the next upright image only very little. By using +several prisms one after the other (see Fig. 21), these upright coloured +lines are separated more and more till we get a very long band or +spectrum. Yet, as you know from our experiments with the light of a +glowing wire or of molten iron, however much you spread out the light +given by a solid or liquid, you can never separate these coloured lines +from each other. It is only when you throw the light of a glowing gas or +vapour into the slit that you get a few bright lines standing out alone. +This is because _all_ the rays of white light are present in glowing +solids and liquids, and they follow each other too closely to be +separated. But a gas, such as glowing hydrogen for example, gives out +only a few separate rays, which, pouring through the slit, throw red, +greenish-blue, and dark blue lines on the screen. Thus you have seen the +double, orange-yellow sodium line (3, Plate I.) which starts out at once +when salt is held in a flame and its light thrown into the spectroscope, +and the red line of potassium vapour under the same treatment; and we +shall observe these again when we study the coloured lights of the sun +and stars." + +[Illustration: Fig. 20. + +Kirchhoff's spectroscope. + +A, The telescope which receives the ray of light through the slit in O.] + +[Illustration: Fig. 21. + +Passage of rays through the spectroscope. + +S, S', Slit through which the light falls on the prisms. 1, 2, 3, 4, +Prisms in which the rays are dispersed more and more. _a_, _b_, Screen +receiving the spectrum, of which the seven principal colours are +marked.] + +"We see, then, that the work of our magic glass, the spectroscope, is +simply to sift the waves of light, and that these waves, from their +colour and their position in the long spectrum, actually tell us what +glowing gases have started them on their road. Is not this like magic? +I take a substance made of I know not what; I break it up, and, melting +it in the intense heat of an electric spark, throw its light into the +spectroscope. Then, as I examine this light after it has been spread out +by the prisms, I can actually read by unmistakable lines what metals or +non-metals it contains. Nay, more; when I catch the light of a star, or +even of a faint nebula, in my telescope, and pass it through these +prisms, there, written up on the magic-coloured band, I read off the +gases which are glowing in that star-sun or star-dust billions of miles +away. + +"Now, boys, I have let you into the secrets of my five magic +glasses--the magnifying-glass, the microscope, the telescope, the +photographic camera, and the spectroscope. With these and the help of +chemistry you can learn to work all my spells. You can peep into the +mysteries of the life of the tiniest being which moves unseen under your +feet; you can peer into that vast universe, which we can never visit so +long as our bodies hold us down to our little earth; you can make the +unseen stars print their spots of light on the paper you hold in your +hand, by means of light-waves, which left them hundreds of years ago; or +you can sift this light in your spectroscope, and make it tell you what +substances were glowing in that star when they were started on their +road. All this you can do on one condition, namely, that you seek +patiently to know the truth. + +"Stories of days long gone by tell us of true magicians and false +magicians, and the good or evil they wrought. Of these I know nothing, +but I do know this, that the value of the spells you can work with my +magic glasses depends entirely upon whether you work patiently, +accurately, and honestly. If you make careless, inaccurate experiments, +and draw hasty conclusions, you will only do bad work, which it may take +others years to undo; but if you question your instruments honestly and +carefully, they will answer truly and faithfully. You may make many +mistakes, but one experiment will correct the other; and while you are +storing up in your own mind knowledge which lifts you far above this +little world, or enables you to look deep below the outward surface of +life, you may add your little group of facts to the general store, and +help to pave the way to such grand discoveries as those of Newton in +astronomy, Bunsen and Kirchhoff in spectrum analysis, and Darwin in the +world of life." + + + + +CHAPTER III + +FAIRY RINGS AND HOW THEY ARE MADE + + +[Illustration] + +It was a lovely warm day in September, the golden corn had been cut and +carted, and the waggons of the farmers around were free for the use of +the college lads in their yearly autumn holiday. There they stood in a +long row, one behind the other in the drive round the grounds, each with +a pair of sleek, powerful farm-horses, and the waggoners beside them +with their long whips ornamented with coloured ribbons; and as each +waggon drew up before the door, it filled rapidly with its merry load +and went on its way. + +They had a long drive of seven miles before them, for they were going to +cross the wild moor, and then descend gradually along a fairly good road +to the more wooded and fertile country. Their object that day was to +reach a certain fairy dell known to a few only among the party as one of +the loveliest spots in Devon. It was a perfect day for a picnic. As they +drove over the wide stretches of moorland, with tors to right and tors +to the left, the stunted furze bushes growing here and there glistened +with spiders' webs from which the dew had not yet disappeared, and +mosses in great variety carpeted the ground, from the lovely +thread-mosses, with their scarlet caps, to the pale sphagnum of the +bogs, where a halt was made for some of the botanists of the party to +search for the little Sundew (_Drosera rotundifolia_). Though this +little plant had now almost ceased to flower, it was not difficult to +recognise by its rosette of leaves glistening with sticky glands which +it spreads out in many of the Dartmoor bogs to catch the tiny flies and +suck out their life's blood, and several specimens were uprooted and +carefully packed away to plant in moist moss at home. + +From this bog onwards the road ran near by one of the lovely streams +which feed the rivers below, and, passing across a bridge covered with +ivy, led through a small forest of stunted trees round which the +woodbine clung, hanging down its crimson berries, and the bracken fern, +already putting on its brown and yellow tints, grew tall and thick on +either side. Then, as they passed out of the wood, they came upon the +dell, a piece of wild moorland lying in a hollow between two granite +ridges, with large blocks of granite strewn over it here and there, and +furze bushes growing under their shelter, still covered with yellow +blossoms together with countless seed-bearing pods, which the +youngsters soon gathered for the shiny-black seeds within them. + +Here the waggons were unspanned, the horses tethered out, the food +unpacked, and preparations for the picnic soon in full swing. Just at +this moment, however, a loud shout from one part of the dell called +every one's attention. "The fairy rings! the fairy rings! we have found +the fairy rings!" and there truly on the brown sward might be seen three +delicate green rings, the fresh sprouting grass growing young and tender +in perfect circles measuring from six feet to nearly three yards across. + +"What are they?" The question came from many voices at once, but it was +the Principal who answered. + +"Why, do you not know that they are pixie circles, where the 'elves of +hills, brooks, standing lakes, and groves' hold their revels, whirling +in giddy round, and making the rings, 'whereof the ewe not bites'? Have +you forgotten how Mrs. Quickly, in the _Merry Wives of Windsor_, tells +us that + + "'nightly, meadow-fairies, look you sing, + Like to the Garter's compass, in a ring: + The expressure that it bears, green let it be, + More fertile-fresh than all the field to see'? + +"If we are magicians and work spells under magic glasses, why should not +the pixies work spells on the grass? I brought you here to-day on +purpose to see them. Which of you now can name the pixie who makes +them?" + +A deep silence followed. If any knew or guessed the truth of the matter, +they were too shy to risk making a mistake. + +"Be off with you then," said the Principal, "and keep well away from +these rings all day, that you may not disturb the spell. But come back +to me before we return at night, and perhaps I may show you the +wonder-working pixie, and we may take him home to examine under the +microscope." + +The day passed as such happy days do, and the glorious harvest moon had +risen over the distant tors before the horses were spanned and the +waggons ready. But the Principal was not at the starting place, and +looking round they saw him at the farther end of the dell. + +"Gently, gently," he cried, as there was one general rush towards him; +"look where you tread, for I stand within a ring of fairies!" + +And then they saw that just outside the green circle in which he stood, +forming here and there a broken ring, were patches of a beautiful tiny +mushroom, each of which raised its pale brown umbrella in the bright +moonlight. + +"Here are our fairies, boys. I am going to take a few home where they +can be spared from the ring, and to-morrow we will learn their history." + + * * * * * + +The following day saw the class-room full, and from the benches eager +eyes were turned to the eight windows, in each of which stood one of the +elder boys at his microscope ready for work. For under those microscopes +the Principal always arranged some object referred to in his lecture and +figured in diagrams on the walls, and it was the duty of each boy, after +the lecture was over, to show and explain to the class all the points +of the specimen under his care. These boys were always specially envied, +for though the others could, it is true, follow all the descriptions +from the diagrams, yet these had the plant or animal always under their +eye. Discussion was at this moment running high, for there was a great +uncertainty of opinion as to whether a mushroom could be really called a +plant when it had no leaves or flowers. All at once the hush came, as +the Principal stepped into his desk and began:-- + +"Life is hard work, boys, and there is no being in this world which has +not to work for its living. You all know that a plant grows by taking in +gases and water, and working them up into sap and living tissue by the +help of the sunshine and the green matter in their leaves; and you know, +too, that the world is so full of green plants that hundreds and +thousands of young seedlings can never get a living, but are stifled in +their babyhood or destroyed before they can grow up. + +"Now there are many dark, dank places in the world where plants cannot +get enough sunlight and air to make green colouring matter and +manufacture their own food. And so it comes to pass that a certain class +of plants have found another way of living, by taking their food ready +made from other decaying plants and animals, and so avoiding the +necessity of manufacturing it for themselves. These plants can live +hidden away in dark cellars and damp cupboards, in drains and pipes +where no light ever enters, under a thick covering of dead leaves in the +forest, under fallen trunks and mossy stones; in fact, wherever +decaying matter, whether of plant or animal, can be found for them to +feed upon. + +"It is to this class, called _fungi_, which includes all mushrooms and +moulds, mildews, smuts, and ferments, that the mushroom belongs which we +found yesterday making the fairy rings. And, in truth, we were not so +far wrong when we called them pixies or imps, for many of them are +indeed imps of mischief, which play sorry pranks in our stores at home +and in the fields and forest abroad. They grow on our damp bread, or +cheese, or pickles; they destroy fruit and corn, hop and vine, and even +take the life of insects and other animals. Yet, on the other hand, they +are useful in clearing out unhealthy nooks and corners, and purifying +the air; and they can be made to do good work by those who know how to +use them; for without ferments we could have neither wine, beer, nor +vinegar, nor even the yeast which lightens our bread. + +"I am going to-day to introduce you to this large vagabond class of +plants, that we may see how they live, grow, and spread, what good and +bad work they do, and how they do it. And before we come to the +mushrooms, which you know so well, we must look at the smaller forms, +which do all their work above ground, so that we can observe them. For +the _fungi_ are to be found almost everywhere. The film growing over +manure-heaps, the yeast plant, the wine fungus, and the vinegar plant; +the moulds and mildews covering our cellar-walls and cupboards, or +growing on decayed leaves and wood, on stale fruit, bread, or jam, or +making black spots on the leaves of the rose, the hop, or the vine; the +potato fungus, eating into the potato in the dark ground and producing +disease; the smut filling the grains of wheat and oats with disease, the +ergot feeding on the rye, the rust which destroys beetroot, the rank +toadstools and puffballs, the mushroom we eat, and the truffles which +form even their fruit underground,--all these are _fungi_, or lowly +plants which have given up making their own food in the sunlight, and +take it ready made from the dung, the decaying mould, the root, the +leaf, the fruit, or the germ on which they grow. Lastly, the diseases +which kill the silkworm and the common house-fly, and even some of the +worst skin diseases in man, are caused by minute plants of this class +feeding upon their hosts." + +[Illustration: Fig. 22. + +Three forms of vegetable mould magnified. + +1, _Mucor Mucedo_. 2, _Aspergillus glaucus_. 3, _Penicillium glaucum_.] + +"In fact, the _fungi_ are so widely spread over all things living and +dead, that there is scarcely anything free from them in one shape or +another. The minute spores, now of one kind, now of another, float in +the air, and settling down wherever they find suitable food, have +nothing more to do than to feed, fatten, and increase, which they do +with wonderful rapidity. Let us take as an example one of the moulds +which covers damp leaves, and even the paste and jam in our cupboard. I +have some here growing upon a basin of paste, and you see it forms a +kind of dense white fur all over the surface, with here and there a +bluish-green tinge upon it. This white fur is the common mould, _Mucor +Mucedo_ (1, Fig. 22), and the green mould happens in this case to be +another mould, _Penicillium glaucum_ (3, Fig. 22); but I must warn you +that these minute moulds look very much alike until you examine them +under the microscope, and though they are called white, blue, or green +moulds, yet any one of them may be coloured at different times of its +growth. Another very common and beautiful mould, _Aspergillus glaucus_ +(2, Fig. 22), often grows with Mucor on the top of jam. + +"All these plants begin with a spore or minute colourless cell of living +matter (_s_, Fig. 23), which spends its energy in sending out tubes in +all directions into the leaves, fruit, or paste on which it feeds. The +living matter, flowing now this way now that, lays down the walls of its +tubes as it flows, and by and by, here and there, a tube, instead of +working into the paste, grows upwards into the air and swells at the tip +into a colourless ball in which a number of minute seed-like bodies +called spores are formed. The ball bursts, the spores fall out, and each +one begins to form fresh tubes, and so little by little the mould grows +denser and thicker by new plants starting in all directions. + +"Under the first microscope you will see a slide showing the tubes which +spread through the paste, and which are called the _mycelium_ (_m_, Fig. +23), and amongst it are three upright tubes, one just starting _a_, +another with the fruit ball forming _b_, and a third _c_, which is +bursting and throwing out the spores. The _Aspergillus_ and the +_Penicillium_ differ from the _Mucor_ in having their spores naked and +not enclosed in a spore-case. In _Penicillium_ they grow like the beads +of a necklace one above the other on the top of the upright tube, and +can very easily be separated (see Fig. 22); while _Aspergillus_, a most +lovely silvery mould, is more complicated in the growth of its spores, +for it bears them on many rows branching out from the top of the tube +like the rays of a star." + +[Illustration: Fig. 23. + +_Mucor Mucedo_, greatly magnified. (After Sachs and Brefeld.) + +_m_, Mycelium, or tangle of threads. _a_, _b_, _c_, Upright tubes in +different stages. _c_, Spore-case bursting and sending out spores. _s_, +1, 2, 3, A growing spore, in different stages, starting a new mycelium.] + +"I want you to look at each of these moulds carefully under the +microscope, for few people who hastily scrape a mould away, vexed to +find it on food or damp clothing, have any idea what a delicate and +beautiful structure lies under their hand. These moulds live on decaying +matter, but many of the mildews, rusts, and other kinds of fungus, prey +upon living plants such as the _smut_ of oats (_Ustilago carbo_), and +the _bunt_ (_Tilletia caria_) which eats away the inside of the grains +of wheat, while another fungus attacks its leaves. There is scarcely a +tree or herb which has not one fungus to prey upon it, and many have +several, as, for example, the common lime-tree, which is infested by +seventy-four different fungi, and the oak by no less than 200. + +"So these colourless food-taking plants prey upon their neighbours, +while they take their oxygen for breathing from air. The 'ferments,' +however, which live _inside_ plants or fluids, take even their oxygen +for breathing from their hosts. + +"If you go into the garden in summer and pluck an overripe gooseberry, +which is bursting like this one I have here, you will probably find that +the pulp looks unhealthy and rotten near the split, and the gooseberry +will taste tart and disagreeable. This is because a small fungus has +grown inside, and worked a change in the juice of the fruit. At first +this fungus spread its tubes outside and merely _fed_ upon the fruit, +using oxygen from the air in breathing; but by and by the skin gave way, +and the fungus crept inside the gooseberry where it could no longer get +any fresh air. In this dilemma it was forced to break up the sugar in +the fruit and take the oxygen out of it, leaving behind only alcohol and +carbonic acid which give the fermented taste to the fruit. + +"So the fungus-imp feeds and grows in nature, and when man gets hold of +it he forces it to do the same work for a useful purpose, for the +grape-fungus grows in the vats in which grapes are crushed and kept away +from air, and tearing up the sugar, leaves alcohol behind in the +grape-juice, which in this way becomes wine. So, too, the yeast-fungus +grows in the malt and hop liquor, turning it into beer; its spores +floating in the fluid and increasing at a marvellous rate, as any +housewife knows who, getting yeast for her bread, tries to keep it in a +corked bottle. + +"The yeast plant has never been found wild. It is only known as a +cultivated plant, growing on prepared liquor. The brewer has to sow it +by taking some yeast from other beer, or by leaving the liquor exposed +to air in which yeast spores are floating; or it will sow itself in the +same way in a mixture of water, hops, sugar, and salt, to which a +handful of flour is added. It increases at a marvellous rate, one cell +budding out of another, while from time to time the living matter in a +cell will break up into four parts instead of two, and so four new cells +will start and bud. A drop of yeast will very soon cover a glass slide +with this tiny plant, as you will see under the second microscope, where +they are now at work (Fig. 24)." + +[Illustration: Fig. 24. + +Yeast cells growing under the microscope. _a_, Single cells. _b_, Two +cells forming by division. _c_, A group of cells where division is going +on in all directions.] + +"But perhaps the most curious of all the minute fungi are those which +grow inside insects and destroy them. At this time of year you may +often see a dead fly sticking to the window-pane with a cloudy white +ring round it; this poor fly has been killed by a little fungus called +_Empusa muscae_. A spore from a former plant has fallen perhaps on the +window-pane, or some other spot over which the fly has crawled, and +being sticky has fixed itself under the fly's body. Once settled on a +favourable spot it sends out a tube, and piercing the skin of the fly, +begins to grow rapidly inside. There it forms little round cells one +after the other, something like the yeast-cells, till it fills the whole +body, feeding on its juices; then each cell sends a tube, like the +upright tubes of the _Mucor_ (Fig. 23) out again through the fly's skin, +and this tube bursts at the end, and so new spores are set free. It is +these tubes, and the spores thrown from them, which you see forming a +kind of halo round the dead fly as it clings to the pane. Other fungi in +the same way kill the silkworm and the caterpillars of the cabbage +butterfly. Nor is it only the lower animals which suffer. When we once +realise that fungus spores are floating everywhere in the air, we can +understand how the terrible microscopic fungi called _bacteria_ will +settle on an open wound and cause it to fester if it is not properly +dressed. + +"Thus we see that these minute fungi are almost everywhere. The larger +ones, on the contrary, are confined to the fields and forests, damp +walls and hollow trees; or wherever rotting wood, leaves, or manure +provide them with sufficient nourishment. Few people have any clear +ideas about the growth of a mushroom, except that the part we pick +springs up in a single night. The real fact is, that a whole mushroom +plant is nothing more than a gigantic mould or mildew, only that it is +formed of many different shaped cells, and spreads its tubes +_underground_ or through the trunks of trees instead of in paste or jam, +as in the case of the mould." + +[Illustration: Fig. 25. + +Early stages of the mushroom. (After Sachs.) + +_m_, Mycelium. _b1-3_, Mushroom buds of different ages. _b4_, Button +mushroom. _g_, Gills forming inside before lower attachment of the cap +gives way at _v_.] + +"The part which we gather and call a mushroom, a toadstool, or a +puffball is only the fruit, answering to the round balls of the mould. +The rest of the plant is a thick network of tubes, which you will see +under the third microscope. These tubes spread underground and suck in +decayed matter from the earth; they form the _mycelium_ (_m_, Fig. 25) +such as we found in the mould. The mushroom-growers call it 'mushroom +spawn' because they use it to spread over the ground for new crops. Out +of these underground tubes there springs up from time to time a swollen +round body no bigger at first than a mustard seed (_b1_, Fig. 25). As it +increases in size it comes above ground and grows into the mushroom or +spore-case, answering to the round balls which contain the spores of the +mould. At first this swollen body is egg-shaped, the top half being +largest and broadest, and the fruit is then called a 'button-mushroom' +_b4_. Inside this ball are now formed a series of folds made of long +cells, some of which are soon to bear spores just as the tubes in the +mould did, and while these are forming and ripening, a way out is +preparing for them. For as the mushroom grows, the skin of the lower +part of the ball (_v_, _b4_) is stretched more and more, till it can +bear the strain no longer and breaks away from the stalk; then the ball +expands into an umbrella, leaving a piece of torn skin, called the veil +(_v_, Fig. 26), clinging to the stalk." + +[Illustration: Fig. 26. + +Later stages of the mushroom. (After Gautier.) + +1, Button mushroom stage. _c_, Cap. _v_, Veil. _g_, Gills. + +2, Full-grown mushroom, showing veil v after the cap is quite free, and +the gills or lamellae _g_, of which the structure is shown in Fig. 27.] + +"All this happens in a single night, and the mushroom is complete, with +a stem up the centre and a broad cap, under which are the folds which +bear the spores. Thus much you can see for yourselves at any time by +finding a place where mushrooms grow and looking for them late at night +and early in the morning so as to get the different stages. But now we +must turn to the microscope, and cutting off one of the folds, which +branch out under the cap like the spokes of a wheel, take a slice across +it (1, Fig. 27) and examine." + +[Illustration: Fig. 27. + +1, One of the gills or lamellae of the mushroom slightly magnified, +showing the cells round the edge. _c_, Cells which do not bear spores. +_fc_, Fertile cells. 2, A piece of the edge of the same powerfully +magnified, showing how the spores _s_ grow out of the tip of the fertile +cells _fc_.] + +"First, under a moderate power, you will see the cells forming the +centre of the fold and the layer of long cells (_c_ and _fc_) which are +closely packed all round the edge. Some of these cells project beyond +the others, and it is they which bear the spores. We see this plainly +under a very strong power when you can distinguish the sterile cells _c_ +and the fertile cells _fc_ projecting beyond them, and each bearing +four spore-cells _s_ on four little horns at its tip. + +"These spores fall off very easily, and you can make a pretty experiment +by cutting off a large mushroom head in the early morning and putting it +flat upon a piece of paper. In a few hours, if you lift it very +carefully, you will find a number of dark lines on the paper, radiating +from a centre like the spokes of a wheel, each line being composed of +the spores which have fallen from a fold as it grew ripe. They are so +minute that many thousands would be required to make up the size of the +head of an ordinary pin, yet if you gather the spores of the several +kinds of mushroom, and examine them under a strong microscope, you will +find that even these specks of matter assume different shapes in the +various species. + +"You will be astonished too at the immense number of spores contained in +a single mushroom head, for they are reckoned by millions; and when we +remember that each one of these is the starting point of a new plant, it +reminds us forcibly of the wholesale destruction of spores and seeds +which must go on in nature, otherwise the mushrooms and their companions +would soon cover every inch of the whole world. + +"As it is, they are spread abroad by the wind, and wherever they escape +destruction they lie waiting in every nook and corner till, after the +hot summer, showers of rain hasten the decay of plants and leaves, and +then the mushrooms, toadstools, and puffballs, grow at an astounding +pace. If you go into the woods at this season you may see the enormous +deep-red liver fungus (_Fistulina hepatica_) growing on the oak-trees, +in patches which weigh from twenty to thirty pounds; or the glorious +orange-coloured fungus (_Tremella mesenterica_) growing on bare sticks +or stumps of furze; or among dead leaves you may easily chance on the +little caps of the crimson, scarlet, snowy white, or orange-coloured +fungi which grow in almost every wood. From white to yellow, yellow to +red, red to crimson and purple black, there is hardly any colour you may +not find among this gaily-decked tribe; and who can wonder that the +small bright-coloured caps have been supposed to cover tiny imps or +elves, who used the large mushrooms to serve for their stools and +tables? + +"There they work, thrusting their tubes into twigs and dead branches, +rotting trunks and decaying leaves, breaking up the hard wood and tough +fibres, and building them up into delicate cells, which by and by die +and leave their remains as food for the early growing plants in the +spring. So we see that in their way the mushrooms and toadstools are +good imps after all, for the tender shoot of a young seedling plant +could take no food out of a hard tree-trunk, but it finds the work done +for it by the fungus, the rich nourishment being spread around its young +roots ready to be imbibed. + +"To find our fairy-ring mushrooms, however, we must leave the wood and +go out into the open country, especially on the downs and moors and +rough meadows, where the land is poor and the grass coarse and spare. +There grow the nourishing kinds, most of which we can eat, and among +these is the delicate little champignon or 'Scotch-bonnet' mushroom, +_Marasmius Oreades_,[1] which makes the fairy-rings. When a spore of +this mushroom begins to grow, it sucks up vegetable food out of the +earth and spreads its tubes underground, in all directions from the +centre, so that the mycelium forms a round patch like a thick +underground circular cobweb. In the summer and autumn, when the weather +is suitable, it sends up its delicate pale-brown caps, which we may +gather and eat without stopping the growth of the plant. + + [1] Shown in initial letter of this chapter. + +"This goes on year after year underground, new tubes always travelling +outwards till the circle widens and widens like the rings of water on a +pond, only that it spreads very slowly, making a new ring each year, +which is often composed of a mass of tubes as much as a foot thick in +the ground, and the tender tubes in the centre die away as the new ones +form a larger hoop outside. + +"But all this is below ground; where then are our fairy rings? Here is +the secret. The tubes, as we have seen, take up food from the earth and +build it up into delicate cells, which decay very soon, and as they die +make a rich manure at the roots of the grass. So each season the cells +of last year's ring make a rich feeding-ground for the young grass, +which springs up fresh and green in a fairy ring, while _outside_ this +emerald circle the mushroom tubes are still growing and increasing +underneath the grass, so that next year, when the present ring is no +longer richly fed, and has become faded and brown like the rest of the +moor, another ring will spring up outside it, feeding on the prepared +food below." + +"In bad seasons, though the tubes go on spreading and growing below, the +mushroom fruit does not always appear above ground. The plant will only +fruit freely when the ground has been well warmed by the summer sun, +followed by damp weather to moisten it. This gives us a rich crop of +mushrooms all over the country, and it is then you can best see the ring +of fairy mushrooms circling outside the green hoop of fresh grass. In +any case the early morning is the time to find them; it is only in very +sheltered spots that they sometimes last through the day, or come up +towards evening, as I found them last night on the warm damp side of the +dell. + +"This is the true history of fairy rings, and now go and look for +yourselves under the microscopes. Under the first three you will find +the three different kinds of mould of our diagram (Fig. 22). Under the +fourth the spores of the mould are shown in their first growth putting +out the tubes to form the mycelium. The fifth shows the mould itself +with its fruit-bearing tubes, one of which is bursting. Under the sixth +the yeast plant is growing; the seventh shows a slice of one of the +folds of the common mushroom with its spore-bearing horns; and under the +eighth I have put some spores from different mushrooms, that you may see +what curious shapes they assume. + +"Lastly, let me remind you, now that the autumn and winter are coming, +that you will find mushrooms, toadstools, puffballs, and moulds in +plenty wherever you go. Learn to know them, their different shapes and +colours, and above all the special nooks each one chooses for its home. +Look around in the fields and woods and take note of the decaying plants +and trees, leaves and bark, insects and dead remains of all kinds. Upon +each of these you will find some fungus growing, breaking up their +tissues and devouring the nourishing food they provide. Watch these +spots, and note the soft spongy soil which will collect there, and then +when the spring comes, notice what tender plants flourish upon these +rich feeding grounds. You will thus see for yourselves that the fungi, +though they feed upon others, are not entirely mischief-workers, but +also perform their part in the general work of life." + + + + +CHAPTER IV + +THE LIFE-HISTORY OF LICHENS AND MOSSES + + +[Illustration] + +The autumn has passed away and we are in the midst of winter. In the +long winter evenings the stars shine bright and clear, and tempt us to +work with the telescope and its helpmates the spectroscope and +photographic plates. But at first sight it would seem as though our +microscopes would have to stand idle so far at least as plants are +concerned, or be used only to examine dried specimens and mounted +sections. Yet this is not the fact, as I remembered last week when +walking through the bare and leafless wood. A startled pheasant rising +with a whirr at the sound of my footsteps among the dead leaves roused +me from my thoughts, and as a young rabbit scudded across the path and I +watched it disappear among the bushes, I was suddenly struck with the +great mass of plant life flourishing underfoot and overhead. + +Can you guess what plants these were? I do not mean the evergreen pines +and firs, nor the few hardy ferns, nor the lovely ivy clothing the +trunks of the trees. Such plants as these live and remain green in the +winter, but they do not grow. If you wish to find plant life revelling +in the cold damp days of winter, fearing neither frost nor snow and +welcoming mist and rain, you must go to the mosses, which as autumn +passes away begin to cover the wood-paths, to creep over the roots of +the trees, to suck up the water in the bogs, and even to clothe dead +walls and stones with a soft green carpet. And with the mosses come the +lichens, those curious grey and greenish oddities which no one but a +botanist would think of classing among plants. + +The wood is full of them now: the hairy lichens hang from the branches +of many of the trees, making them look like old greybearded men; the +leafy lichens encircle the branches, their pale gray, green, and yellow +patches looking as if they were made of crumpled paper cut into wavy +plates; and the crusty lichens, scarcely distinguishable from the bark +of the trees, cover every available space which the mosses have left +free. + +As I looked at these lichens and thought of their curious history I +determined that we would study them to-day, and gathered a basketful of +specimens (see Fig. 28). But when I had collected these I found I had +not the heart to leave the mosses behind. I could not even break off a +piece of bark with lichen upon it without some little moss coming too, +especially the small thread-mosses (_Bryum_) which make a home for +themselves in every nook and corner of the branches; while the +feather-mosses, hair-mosses, cord-mosses, and many others made such a +lovely carpet under my feet that each seemed too beautiful to pass by, +and they found their way into my basket, crowned at the top with a large +mass of the pale-green Sphagnum, or bog-moss, into which I sank more +than ankle-deep as I crossed the bog in the centre of the wood on my way +home. + +[Illustration: Fig. 28. + +Examples of Lichens. (From life.) + +1, A hairy lichen. 2, A leafy lichen. 3, A crustaceous lichen. _f_, _f_, +the fruit.] + +So here they all are, and I hope by the help of our magic glass to let +you into some of the secrets of their lives. It is true we must study +the structure of lichens chiefly by diagrams, for it is too minute for +beginners to follow under the microscope, so we must trust to drawings +made by men more skilful in microscopic botany, at any rate for the +present. But the mosses we can examine for ourselves and admire their +delicate leaves and wonderful tiny spore-cases. + +Now the first question which I hope you want to ask is, how it is that +these lowly plants flourish so well in the depth of winter when their +larger and stronger companions die down to the ground. We will answer +this first as to the lichens, which are such strange uncanny-looking +plants that it is almost difficult to imagine they are alive at all; and +indeed they have been a great puzzle to botanists. + +[Illustration: Fig. 29. + +Single-celled green plants growing and dividing (_Pleurococcus_). (After +Thuret and Bornet.)] + +Before we examine them, however, look for a minute at a small drop of +this greenish film which I have taken from the rain-water taken outside. +I have put some under each microscope, and those who can look into them +will see the slide almost covered with small round green cells very much +like the yeast cells we saw when studying the Fungi, only that instead +of being colourless they are a bright green. Some of these cells will I +suspect be longer than others, and these long cells will be moving over +the slide very rapidly, swimming hither and thither, and you will see, +perhaps for the first time, that very low plants can swim about in +water. These green cells are, indeed, the simplest of all plants, and +are merely bags of living matter which, by the help of the green +granules in them, are able to work up water and gases into nourishing +food, and so to live, grow, and multiply. + +There are many kinds of these single-celled plants in the world. You may +find them on damp paths, in almost any rain-water butt, in ponds and +ditches, in sparkling waterfalls, along the banks of flowing rivers, and +in the cold clear springs on the bleak mountains. Some of them take the +form of tangled threads[1] composed of long strings of cells, and these +sometimes form long streamers in flowing water, and at other times are +gathered together in a shapeless film only to be disentangled under a +microscope. Other kinds[2] wave to and fro on the water, forming dense +patches of violet, orange-brown, or glossy green scum shining in the +bright sunlight, and these flourish equally in the ponds of our gardens +and in pools in the Himalaya mountains, 18,000 feet above the sea. +Others again[3] seize on every damp patch on tree trunks, rocks, or +moist walls, covering them with a green powder formed of single plant +cells. Other species of this family turn a bright red colour when the +cells are still; and one, under the name of Gory Dew,[4] has often +frightened the peasants of Italy, by growing very rapidly over damp +walls and then turning the colour of blood. Another[5] forms the "red +snow" of the Arctic regions, where it covers wide surfaces of snow with +a deep red colour. Others[6] form a shiny jelly over rocks and stones, +and these may be found almost everywhere, from the garden path to the +warm springs of India, from the marshes of New Zealand up to the shores +of the Arctic ocean, and even on the surface of floating icebergs. + + [1] _Confervae._ + + [2] _Oscillariae._ + + [3] _Protococcus._ + + [4] _Palmella cruenta._ + + [5] _Protococcus nivalis._ + + [6] _Nostoc._ + +The reason why these plants can live in such very different regions is +that they do not take their food through roots out of the ground, but +suck in water and gases through the thin membrane which covers their +cell, and each cell does its own work. So it matters very little to them +where they lie, so long as they have moisture and sunlight to help them +in their work. Wherever they are, if they have these, they can take in +carbonic acid from the air and work up the carbon with other gases which +they imbibe with the water, and so make living material. In this way +they grow, and as a cell grows larger the covering is stretched and part +of the digested food goes to build up more covering membrane, and by and +by the cell divides into two and each membrane closes up, so that there +are two single-celled plants where there was only one before. This will +sometimes go on so fast that a small pond may be covered in a few hours +with a green film formed of new cells. + +Now we have seen, when studying mushrooms, that the one difference +between these green plants and the single-celled Fungi is that while the +green cells make their own food, colourless cells can only take it in +ready-made, and therefore prey upon all kinds of living matter. This is +just what happens in the lichens; and botanists have discovered that +these curious growths are really the result of a _partnership_ between +single-celled green plants and single-celled fungi. The grey part is a +fungus; but when it is examined under the microscope we find it is not a +fungus only; a number of green cells can be seen scattered through it, +which, when carefully studied, prove to be some species of the green +single-celled plants. + +Here are two drawings of sections cut through two different lichens, and +enormously magnified so that the cells are clearly seen. 1, Fig. 30 is +part of a hairy lichen (1, Fig. 28), and 2 is part of a leafy lichen (2, +Fig. 28). The hairy lichen as you see has a row of green cells all round +the tiny branch, with fungus cells on all sides of them. The leafy +lichen, which only presents one surface to the sun and air while the +other side is against the tree, has only one layer of green cells near +the surface, but protected by the fungus above. + +[Illustration: Fig. 30. + +Sections of Lichens. (Sachs.) + +1, Section of a hairy lichen, _Usnea barbata_. 2, Section of a leafy +lichen, _Sticta fuliginosa_. 3, Early growth of a lichen. _gc_, Green +cells. _f_, Fungus.] + +The way the lichen has grown is this. A green cell (_gc_ 3, Fig. 30) +falling on some damp spot has begun to grow and spread, working up food +in the sunlight. To it comes the spore of the fungus _f_, first +thrusting its tubes into the tree-bark, or wall, and then spreading +round the green cells, which remain always in such a position that +sunlight, air, and moisture can reach them. From this time the two +classes of plants live as friends, the fungus using part of the food +made by the green cells, and giving them in return the advantage of +being spread out to the sunlight, while they are also protected in +frosty or sultry weather when they would dry up on a bare surface. On +the whole, however, the fungus probably gains the most, for it has been +found, as we should expect, that the green cells can live and grow if +separated out of the lichen, but the fungus cells die when their +industrious companions are taken from them. + +At any rate the partnership succeeds, as you will see if you go into the +wood, or into an orchard where the apple-trees are neglected, for every +inch of the branches is covered by lichens if not already taken up by +mosses or toadstools. + +There is hardly any part of the world except the tropics where lichens +do not abound. In the Alps of Scandinavia close to the limits of +perpetual snow, in the sandy wastes of Arctic America, and over the +dreary Tundras of Arctic Siberia, where the ground is frozen hard during +the greater part of the year, they flourish where nothing else can live. + +The little green cells multiply by dividing, as we saw them doing in the +green film from the water-butt. The fungus, however, has many different +modes of seeding itself. One of these is by forming little pockets in +the lichen, out of which, when they burst, small round bodies are +thrown, which cover the lichen with a minute green powder. There is +plenty of this powder on the leafy lichen which you have by you. You can +see it with the magnifying-glass, without putting it under the +microscope. As long as the lichen is dry these round bodies do not grow, +but as soon as moisture reaches them they start away and become new +plants. + +[Illustration: Fig. 31. + +Fructification of a lichen. (From Sachs and Oliver.) + +Apothecium or spore-chamber of a lichen. 1, Closed. 2, Open. 3, The +spore-cases and filaments enlarged, showing the spores. _f_, Filaments. +_sc_, Spore-cases. _s_, Spores.] + +A more complicated and beautiful process is shown in this diagram (Fig. +31). If you look carefully at the leafy lichen (2, Fig. 28) you will +find here and there some little cups _f_, while others grow upon the +tips of the hairy lichen. These cups, or fruits, were once closed, +flask-shaped chambers (1, Fig. 31) inside which are formed a number of +oval cells _sc_, which are spore-cases, with from four to eight spores +or seed-like bodies _s3_ inside them. When these chambers, which are +called _apothecia_, are ripe, moist or rainy weather causes them to +swell at the top, and they burst open and the spore-cases throw out the +spores to grow into new fungi. + +In some lichens the chambers remain closed and the spores escape through +a hole in the top, and they are then called _perithecia_, while in +others, as these which we have here, they open out into a cup-shape. + +This, then, is the curious history of lichens; the green cells and fungi +flourishing together in the damp winter and bearing the hardest frost +far better than the summer drought, so that they have their good time +when most other plants are dead or asleep. Yet though some of them, such +as the hairy lichens, almost disappear in the summer, they are by no +means dead, for, like all these very low plants, they can bear being +dried up for a long time, and then, when moisture visits them again, +each green cell sets to work, and they revive. There is much more to be +learnt about them, but this will be sufficient to make you feel an +interest in their simple lives, and when you look for them in the wood +you will be surprised to find how many different kinds there are, for it +is most wonderful that such lowly plants should build up such an immense +variety of curious and grotesque forms. + + * * * * * + +And yet, when we turn to the mosses, I am half afraid they will soon +attract you away from the dull grey lichens, for of all plant histories +it appears to me that the history of the moss-plant is most fascinating. + +As this history is complicated by the moss having, as it were, two +lives, you must give me your whole attention, and I will explain it +first from diagrams, though you can see all the steps under the +microscope. + +Take in your hands, in the first place, a piece of this green moss which +I have brought. How thick it is, like a rich felted carpet! and yet, if +you pull it apart carefully, you will find that each leafy stem is +separate, and can be taken away from the others without breaking +anything. In this dense moss each stem is single and clothed with leaves +wrapped closely round it (see Fig. 33); in some mosses the stem is +branched, and in others the leaves grow on side stalks, as in this +feathery moss (Fig. 32). But in each case every stem is like a separate +plant, with its own tuft of tender roots _r_. + +[Illustration: Fig. 32. + +A stem of feathery moss. (From life.) + +_l_, Leaves. _s_, Stem. _r_, Roots.] + +What a delicate growth it is! The stem is scarcely more than a fine +thread, the leaves minute, transparent, and tender. In this pale +sphagnum or bog-moss (Fig. 36, p. 93), which is much larger and stouter, +you can see better how each one of these leaves, though they are so +thickly packed, is placed so that it can get the utmost light, air, and +moisture. Yet so closely are the leaves of each stem entangled in those +of the next that the whole forms a thick springy green carpet under our +feet. + +How is it, then, that these moss stems, though each independent, grow in +such a dense mass? Partly because moss multiplies so rapidly that new +stems are always thrusting themselves up to the light, but chiefly +because the stems were not always separate, but in very early life +sprang from a common source. + +If, instead of bringing the moss home and tearing it apart, you went to +a spot in the wood where fresh moss was growing, and looked very +carefully on the surface of the ground or among the water of a marsh, +you would find a spongy green mass below the growing moss, very much +like the green scum on a pond. This film, some of which I have brought +home, is seen under the microscope to be a mass of tangled green threads +(_t_, Fig. 34, p. 88) like those of the _Confervae_ (see p. 79), composed +of rows of cells, while here and there upon these threads you would find +a bud (_mb_, Fig. 34) rising up into the air. + +This tangled mass of green threads, called the _protonema_, is the first +growth, from which the moss stems spring. It has itself originated from +a moss-spore; as we shall see by and by. As soon as it has started it +grows and spreads very rapidly, drinking in water and air through all +its cells and sending up the moss buds which swell and grow, giving out +roots below and fine stems above, which soon become crowded with leaves, +forming the velvety carpet we call moss. Meanwhile the soft threads +below die away, giving up all their nourishment to the moss-stems, and +this is why, when you take up the moss, you find each stem separate. But +now comes the question, How does each stem live after the nourishing +threads below have died? It is true each stem has a few hairy roots, +but these are very feeble, and not at all like the roots of higher +plants. The fact is, the moss is built up entirely of tender cells, like +the green cells in the lichen, or in the film upon the pond. These cells +are not shut in behind a thick skin as in the leaves of higher plants, +but have every one of them the power to take in water and gases through +their tender membrane. + +I made last night a rough drawing of the leaf of the feathery moss put +under the microscope, but you will see it far better by putting a leaf +with a little water on a glass slide under the covering glass and +examining it for yourself. You will see that it is composed of a number +of oval-shaped cells packed closely together (_c_ Fig. 33), with a few +long narrow ones _mr_ in the middle of the leaf forming the midrib. +Every cell is as clear and distinct as if it were floating in the water, +and the tiny green grains which help it to work up its food are clearly +visible. + +[Illustration: Fig. 33. + +Moss-leaf magnified. (From life.) + +Showing the cells _c_, each of which can take in and work up its own +food. _mr_, Long cells of the mid-rib.] + +Each of these cells can act as a separate plant, drinking in the water +and air it needs, and feeding and growing quite independently of the +roots below. Yet at the same time the moss stem has a great advantage +over single-celled plants in having root-hairs, and being able to grow +upright and expose its leaves to the sun and air. + +Now you will no longer wonder that moss grows so fast and so thick, and +another curious fact follows from the independence of each cell, namely, +that new growths can start from almost any part of the plant. For +example, pieces will often break off from the tangled mass or protonema +below, and, starting on their own account, form other thread masses. +Then, after the moss stems have grown, a new mass of threads may grow +from one of the tiny root-hairs of a stem and make a fresh tangle; nay, +a thread will sometimes even spring out of a damp moss leaf and make a +new beginning, while the moss stems themselves often put forth buds and +branches, which grow root-hairs and settle down on their own account. + +[Illustration: Fig. 34. + +Polytrichum commune. A large hair-moss. + +_t_, _t_, Threads of green cells forming the _protonema_ out of which +moss-buds spring. _mb_, Buds of moss-stems. _a_, Minute green flower in +which the antherozoids are formed (enlarged in Fig. 35). _p_, _p1_, +_p2_, _p3_, Minute green flower in which the ovules are formed, and +urn-plant springing out of it (enlarged in Fig. 35). _us_, Urn stems. +_c_, Cap. _u_, Urn after cap has fallen off, still protected by its +lid.] + +All this comes from the simple nature of the plants, each cell doing its +own work. Nor are the mosses in any difficulty as to soil, for as the +matted threads decay they form a rich manure, and the dying moss-stems +themselves, being so fragile, turn back very readily into food. This is +why mosses can spread over the poorest soil where even tough grasses +cannot live, and clothe walls and roofs with a rich green. + +[Illustration: Fig. 35. + +Fructification of a moss. + +A, Male moss-flower stripped of its outer leaves, showing jointed +filaments and oval sacs os and antherozoid cells _zc_ swarming out of a +sac. _zc'_, Antherozoid cell enlarged. _z_, Free antherozoid. P, Female +flower with bottle-shaped sacs _bs_. _bs-c_, Bottle-shaped sac, with cap +being pushed up. _u_, Urn of _Funaria hygrometrica_, with small cap. +_u'_, Urn, from which the cap has fallen, showing the teeth _t_ which +keep in the spores.] + +So far, then, we now understand the growth of the mossy-leaf stems, but +this is only half the life of the plant. After the moss has gone on +through the damp winter spreading and growing, there appear in the +spring or summer tiny moss flowers at the tip of some of the stems. +These flowers (_a_, _p_, Fig. 34) are formed merely of a few green +leaves shorter and stouter than the rest, enclosing some oval sacs +surrounded by jointed hairs or filaments (see A and P, Fig. 35). These +sacs are of two different kinds, one set being short and stout _os_, the +others having long necks like bottles _bs_. Sometimes these two kinds of +sac are in one flower, but more often they are in separate flowers, as +in the hair-moss, _Polytrichum commune_ (_a_ and _p_, Fig. 34). Now when +the flowers are ripe the short sacs in the flower A open and fling out +myriads of cells _zc_, and these cells burst, and forth come tiny +wriggling bodies _z_, called by botanists _antherozoids_, one out of +each cell. These find their way along the damp moss to the flower P, and +entering the neck of one of the bottle-shaped sacs _bs_, find out each +another cell or _ovule_ inside. The two cells together then form a +_plant-egg_, which answers to the germ in the seeds of higher plants. + +Now let us be sure we understand where we are in the life of the plant. +We have had its green-growing time, its flowering, and the formation of +what we may roughly call its seed, which last in ordinary higher plants +would fall down and grow into a new green plant. But with the moss there +is more to come. The egg does not shake out of the bottle-necked sac, +but begins to grow inside it, sending down a little tube into the moss +stem, and using it as other plants use the ground to grow in. + +As soon as it is rooted it begins to form a delicate stem, and as this +grows it pushes up the sac _bs_, stretching the neck tighter and tighter +till at last it tears away below, and the sac is carried up and hangs +like an extinguisher or cap (_c_ Figs. 34, 35) over the top of the stem. +Meanwhile, under this cap the top of the stalk swells into a knob +which, by degrees, becomes a lovely little covered urn _u_, something +like a poppy head, which has within it a number of spores. The growth of +this tiny urn-plant often occupies several months, for you must remember +that it is not merely a fruit, though it is often called so, but a real +plant, taking in food through its tubes below and working for its +living. + +When it is finished it is a most lovely little object (_us_, Fig. 34), +the fine hairlike stalk being covered with a green, yellow, or brilliant +red fool's cap on the top, yet the whole in most mosses is not bigger +than an ordinary pin. You may easily see them in the spring or summer, +or even sometimes in the winter. I have only been able to bring you one +very little one to-day, the _Funaria hygrometrica_, which fruits early +in the year. This moss has only a short cap, but in many mosses they are +very conspicuous. I have often pulled them off as you would pull a cap +from a boy's head. In nature they fall off after a time, leaving the +urn, which, though so small, is a most complicated structure. First it +has an outer skin, with holes or mouths in it which open and close to +let moisture in and out. Then come two layers of cells, then an open +space full of air, in which are the green chlorophyll grains which are +working up food for the tiny plant as the moisture comes in to them. +Lastly, within this again is a mass of tissue, round which grow the +spores which are soon to be sown, and which in _Polytrichum commune_ are +protected by a lid. Even after the extinguisher and the lid have both +fallen off, the spores cannot fall out, for a thick row of teeth (_t_, +Fig. 35) is closed over them like the tentacles of an anemone. So long +as the air is damp these teeth remain closed; it is only in fine dry +weather that they open and the spores are scattered on the ground. +_Funaria hygrometrica_ has no lid under its cap, and after the cap falls +the spores are only protected by the teeth. + +When the spores are gone, the life of the tiny urn-plant is over. It +shrivels and dies, leaving ten, fifteen, or even more spores, which, +after lying for some time on the ground, sprout and grow into a fresh +mass of soft threads. + +So now we have completed the life-history of the moss and come back to +the point at which we started. I am afraid it has been rather a +difficult history to follow step by step, and yet it is perfectly clear +when once we master the succession of growths. Starting from a spore, +the thread-mass or protonema gives rise to the moss-stems forming the +dense green carpet, then the green flowers on some of the leaf-stems +give rise to a plant-egg, which roots itself in the stem, and grows into +a perfect plant without leaves, bearing merely the urn in which fresh +spores are formed, and so the round goes on from year to year. + +There are a great number of different varieties of moss, and they differ +in the shape and arrangement of their stems and leaves, and very much in +the formation of their urns, yet this sketch will enable you to study +them with understanding, and when you find in the wood the nodding caps +of the fruiting plants, some red, some green, some yellow, and some a +brilliant orange, you will feel that they are acquaintances, and by the +help of the microscope may soon become friends. + +Among them one of the most interesting is the sphagnum or bog-moss (Fig. +36), which spreads its thick carpet over all the bogs in the woods. You +cannot miss its little orange-coloured spore-cases if you look closely, +for they contrast strongly with its pale green leaves, out of which they +stand on very short stalks. I wish we could examine it, for it differs +much from other mosses, both in leaves and fruit, but it would take us +too long. At least, however, you must put one of its lovely transparent +leaves under the microscope, that you may see the large air-cells which +lie between the growing cells, and admire the lovely glistening bands +which run across and across their covering membrane, for the sphagnum +leaf is so extremely beautiful that you will never forget it when once +seen. It is through these large cells in the edge of the stem and leaf +that the water rises up from the swamp, so that the whole moss is like a +wet sponge. + +[Illustration: Fig. 36. + +Sphagnum moss from a Devonshire bog. (From life.)] + +And now, before we part, we had better sum up the history of lichens and +mosses. With the lichens we have seen that the secret of success seems +to be mutual help. The green cells provide the food, the fungus cells +form a surface over which the green cells can spread to find sunlight +and moisture, and protection from extremes of heat or cold. With the +mosses the secret lies in their standing on the borderland between two +classes of plant life. On the one hand, they are still tender-celled +plants, each cell being able to live its own life and make its own food; +on the other hand, they have risen into shapely plants with the +beginnings of feeble roots, and having stems along which their leaves +are arranged so that they are spread to the light and air. Both lichens +and mosses keep one great advantage common to all tender-celled plants; +they can be dried up so that you would think them dead, and yet, because +they can work all over their surface whenever heat and moisture reach +them, each cell drinks in food again and the plant revives. So when a +scorching sun, or a dry season, or a biting frost kills other plants, +the mosses and lichens bide their time till moisture comes again. + +In our own country they grow almost everywhere--on walls, on broken +ground, on sand-heaps, on roofs and walls, on trees living and dead, and +over all pastures which are allowed to grow poor and worn out. They +grow, too, in all damp, marshy spots; especially the bog-mosses forming +the peat-bogs which cover a large part of Ireland and many regions in +Scotland; and these same bog-mosses occur in America, New Zealand, and +Australia. + +In the tropics mosses are less abundant, probably because other plants +flourish so luxuriantly; but in Arctic Siberia and Arctic America both +lichens and mosses live on the vast Tundras. There, during the three +short months of summer, when the surface of the ground is soft, the +lichens spread far and wide where all else is lifeless, while in moister +parts the Polytrichums or hair-mosses cover the ground, and in swampy +regions stunted Sphagnums form peat-bogs only a few inches in depth over +the frozen soil beneath. If, then, the lichens and mosses can flourish +even in such dreary latitudes as these, we can understand how they defy +even our coldest winters, appearing fresh and green when the snow melts +away from over them, and leave their cells bathed in water, so that +these lowly plants clothe the wood with their beauty when otherwise all +would be bare and lifeless. + + + + +CHAPTER V + +THE HISTORY OF A LAVA STREAM + + +[Illustration] + +It is now just twenty-two years ago, boys, since I saw a wonderful +sight, which is still so fresh in my mind that I have to look round and +remember that it was before any of you were born, in order to persuade +myself that it can be nearly a quarter of a century since I stood with +my feet close to a flowing stream of red-hot lava. + +It happened in this way. I was spending the winter with friends in +Naples, and we were walking quietly one lovely afternoon in November +along the Villa Reale, the public garden on the sea-shore, when one of +our party exclaimed, "Look at Vesuvius!" We did so, and saw in the +bright sunlight a dense dark cloud rising up out of the cone. The +mountain had been sending out puffs of smoke, with a booming noise, for +several days, but we thought nothing of that, for it had been common +enough for slight eruptions to take place at intervals ever since the +great eruption of 1867. This cloud, however, was far larger and +wider-spread than usual, and as we were looking at it we saw a thin red +line begin some way down the side of the mountain and creep onwards +toward the valley which lies behind the Hermitage near where the +Observatory is built (see Fig. 37). "A crater has broken out on the +slope," said our host; "it will be a grand sight to-night. Shall we go +up and see it?" No sooner proposed than settled, and one of the party +started off at once to secure horses and men before others engaged them. + +[Illustration: Fig. 37. + +Somma. Vesuvius. + +Vesuvius, as seen in eruption by the author, November 1868.] + +It was about eight o'clock in the evening when we started in a carriage +for Resina, and alighting there, with buried Herculaneum under our feet, +mounted our horses and set forward with the guides. Then followed a long +ascent of about two hours and a half through the dark night. Silently +and carefully we travelled on over the broad masses of slaggy lava of +former years, along which a narrow horse-path had been worn; and ever +and anon we heard the distant booming in the crater at the summit, and +caught sight of fresh gleams of light as we took some turning which +brought the glowing peak into view. + +Our object was to get as close as possible to the newly-opened crater in +the mountain-side, and when we arrived on a small rugged plain not far +from the spot, we alighted from our horses, which were growing +frightened with the glare, and walked some distance on foot till we came +to a ridge running down the slope, and upon this ridge the lava stream +was flowing. + +Above our heads hung a vast cloud of vapour which reflected the bright +light from the red-hot stream, and threw a pink glow all around, so +that, where the cloud was broken and we could see the dark sky, the +stars looked white as silver in contrast. We could now trace clearly the +outline of the summit towering above us, and even watch the showers of +ashes and dust which burst forth from time to time, falling back into +the crater, or on to the steep slopes of the cone. + +If the night had not been calm, and such a breeze as there was blowing +away from us, our position would scarcely have been safe; and indeed we +were afterwards told we had been rash. But I would have faced even a +greater risk to see so grand a spectacle, and when the guide helped me +to scramble up on to the ledge, so that I stood with my feet within a +few yards of the lava flow, my heart bounded with excitement. I could +not stay more than a few seconds, for the gases and vapour choked me; +but for that short time it felt like a dream to be standing close to a +river of molten rock, which a few hours before had been lying deep in +the bowels of the earth. Glancing upwards to where this river issued +from the cone in the mountain-side, I saw it first white-hot, then +gradually fading to a glowing red as it crept past my feet; and then +looking down the slope I saw it turn black and gloomy as it cooled +rapidly at the top, while through the cracks which opened here and there +as it moved on, puffs of gas and vapour rose into the air, and the red +lava beneath gleamed through the chinks. + +We did not stay long, for the air was suffocating, but took our way back +to the Hermitage, where another glorious sight awaited us. Some way +above and behind the hill on which the Observatory stands there is, or +was, a steep cliff, and over this the lava stream, now densely black, +fell in its way to the valley below, and as it fell it broke into huge +masses, which heeling over exposed the red-hot lava under the crust, +thus forming a magnificent fiery cascade in which black and red were +mingled in wild confusion. + +This is how I saw a fresh red-hot lava stream. I had ascended the +mountain some years before, when it was comparatively quiet, with only +two small cones in its central crater sending out miniature flows of +lava (see Fig. 38). But the crater was too hot for me to cross over to +these cones, and I could only marvel at the mass of ashes of which the +top of the mountain was composed, and plunge a stick into an old lava +stream to see how hot it still remained below. Peaceful and quiet as the +mountain seemed then, I could never have imagined such a glorious +outburst as that of November 1868 unless I had seen it, and yet this was +quite a small eruption compared to those of 1867 and 1872, which in +their turn were nothing to some of the older eruptions in earlier +centuries. + +[Illustration: Fig. 38. + +The top of Vesuvius in 1864. (After Nasmyth.)] + +Now it is the history of this lava stream which I saw, that we are going +to consider to-day, and you will first want to know where it came from, +and what caused it to break out on the mountain-side. The truth is, that +though we know now a good deal about volcanoes themselves, we know very +little about the mighty cauldrons deep down in the earth from which +they come. Our deepest mines only reach to a depth of a little more than +half a mile, and no borings even have been made beyond three-quarters of +a mile, so that after this depth we are left very much to guesswork. + +We do know that the temperature increases as we go farther down from the +surface, but the increase is very different in different districts--in +some places being five times greater than it is in others at an equal +depth, and it is always greatest in localities where volcanoes have been +active not long before. Now if there were an ocean of melted rock at a +certain distance down below the crust all over the globe, there could +scarcely be such a great difference between one place and another, and +for this and many other reasons geologists are inclined to think that, +from some unknown cause, great heat is developed at special points below +the surface at different times. This would account for our finding +volcanic rocks in almost all parts of the world, even very far away from +where there are any active volcanoes now. + +But, as I have said, we do not clearly know why great reservoirs of +melted rock occur from time to time deep under our feet. We may perhaps +one day find the clue from the fact that nearly all, if not all, +volcanoes occur near to the water's edge, either on the coast of the +great oceans or of some enormous inland sea or lake. But at present all +we can say is, that in certain parts of the globe there must be from +time to time great masses of rock heated till they are white-hot, and +having white-hot water mingled with them. These great masses need not, +however, be liquid, for we know that under enormous pressure white-hot +metals remain solid, and water instead of flashing into steam is kept +liquid, pressing with tremendous force upon whatever keeps it confined. + +But now suppose that for some reason the mass of solid rock and ground +above one of these heated spots should crack and become weak, or that +the pressure from below should become so great as to be more powerful +than the weight above, then the white-hot rock and water quivering and +panting to expand, would upheave and burst the walls of their prison. +Cannot you picture to yourselves how when this happened the rock would +swell into a liquid state, and how the water would force its way upwards +into cracks and fissures expanding into steam as it went. Then would be +heard strange rumbling noises underground, as all these heavily +oppressed white-hot substances upheaved and rent the crust above them. +And after a time the country round, or the ground at the bottom of the +sea, would quake and tremble, till by and by a way out would be found, +and the water flashing into vapour would break and fling up the masses +of rock immediately above the passage it had made for itself, and +following after these would come the molten rock pouring out at the new +opening. + +Such outbursts as these have been seen at sea many times near volcanic +islands. In 1811 a new island called Sabrina was thrown up off St. +Michael's in the Azores, and after remaining a short time was washed +away by the waves. In the same way Graham's Island appeared off the +coast of Sicily in 1831, and as late as 1885 Mr. Shipley saw a +magnificent eruption in the Pacific near the Tonga Islands when an +island about three miles long was formed. + +Another very extraordinary outburst, this time on land, took place in +1538 on the opposite side of the Bay of Naples to where Vesuvius stands. +There, on the shores of the Bay of Baiae, a mountain 440 feet high was +built up in one week, where all had before been quiet in the memory of +man. For two years before the outburst came, rumblings and earthquakes +had alarmed the people, and at last one day the sea drew back from the +shore and the ground sank about fourteen feet, and then on the night of +Sunday, September 29, 1538, it was hurled up again, and steam, fiery +gases, stones, and mud burst forth, driving away the frightened people +from the village of Puzzuoli about two miles distant. For a whole week +jets of lava, fragments of rock, and showers of ashes were poured out, +till they formed the hill now called Monte Nuovo, 440 feet high and +measuring a mile and a half round the base. And there it has remained +till the present day, perfectly quiet after the one great outburst had +calmed down, and is now covered with thickets of stone-pine trees. + +These sudden outbursts show that some great change must occur in the +state of the earth's crust under the spots where they take place, and we +know that eruptions may cease for centuries in any particular place and +then begin afresh quite unexpectedly. Vesuvius was a peaceable mountain +overgrown with trees and vines in the time of the Greeks till in the +year A.D. 79 occurred the terrific outburst which destroyed Herculaneum +and Pompeii, shattering old Vesuvius to pieces, so that only the cliffs +on the northwest remain and are called Somma (see Fig. 37), while the +new Vesuvius has grown up in the lap, as it were, of its old self. Yet +when we visit the cliffs of Somma, and examine the old lava streams in +them, we see that the ancient peaceful mountain was itself built up by +volcanic outbursts of molten rock, and showers of clinkers or scoriae, +long before man lived to record it. + +Meanwhile, when once an opening is made, we can understand how after an +eruption is over, and the steam and lava are exhausted, all quiets down +for awhile, and the melted rock in the crater of the mountain cools and +hardens, shutting in once more the seething mass below. This was the +state of the crater when I saw it in 1864, though small streams still +flowed out of two minute cones; but since then at least one great +outburst had taken place in 1867, and now on this November night, 1868, +the imprisoned gases rebelled once more and forced their way through the +mountain-side. + +At this point we can leave off forming conjectures and really study what +happens; for we do know a great deal about the structure of volcanoes +themselves, and the history of a lava-flow has been made very clear +during the last few years, chiefly by the help of the microscope and +chemical experiments. If we imagine then that on the day of the eruption +we could have seen the inside of the mountain, the diagram (Fig. 39) +will fairly represent what was taking place there. + +[Illustration: Fig. 39. + +Diagrammatic section of an active volcano. + +_a_, Central pipe or funnel. _b_, _b_, Walls of the crater or cup. +_c_, _c_, Dark turbid cloud formed by the ascending globular clouds +_d_, _d_. _e_, Rain-shower from escaped vapour. _f_, _f_, Shower of +blocks, cooled bombs, stones, and ashes falling back on to the cone. +_g_, Lava escaping through a fissure, and pouring out of a cone opened +in the mountain side.] + +In the funnel _a_ which passes down from the crater or cup _b_, _b_, +white-hot lava was surging up, having a large quantity of water and +steam entangled in it. The lava, or melted rock, would be in much the +same state as melted iron-slag is, in the huge blast-furnaces in which +iron-rock is fused, only it would have floating in it great blocks of +solid rock, and rounded stones called bombs which have been formed from +pieces of half-melted rock whirled in air and falling back into the +crater, together with clinkers or scoriae, dust and sand, all torn off +and ground down from the walls of the funnel up which the rush was +coming. And in the pipe of melted rock, forcing the lava upwards, +enormous bubbles of steam and gas _d_, _d_ would be rising up one after +another as bubbles rise in any thick boiling substances, such as boiling +sugar or tar. + +In the morning before the eruption, when only a little smoke was issuing +from the crater, these bubbles rose very slowly through the loaded +funnel and the half-cooled lava in the basin, and the booming noise, +like that of heavy cannon, heard from time to time, was caused by the +bursting of one of these globes of steam at the top of the funnel, as it +brought up with it a feeble shower of stones, dust, and scoriae. +Meanwhile the lava surging below was forcing a passage _g_ for itself in +a weak part of the mountain-side and, just at the time when our +attention was called to Vesuvius, the violent pressure from below rent +open a mouth or crater at _h_, so that the lava began to flow down the +mountain in a steady stream. This, relieving the funnel, enabled the +huge steam bubbles _d_, _d_ to rise more quickly, and to form the large +whitish-grey cloud _c_, into which from time to time the red-hot blocks, +scoriae, and pumice were thrown up by the escaping steam and gases. These +blocks and fragments then fell back again in a fiery shower _f_, _f_ +either into the cup, to be thrown up again by the bursting of the next +bubble, or on to the sides of the cone, making it both broader and +higher. + +Only one feature in the diagram was fortunately absent the evening we +went up, namely, the rain-shower _e_. The night, as I said, was calm, +and the air dry, and the steam floated peacefully away. The next night, +however, when many people hurried down from Rome to see the sight they +were woefully disappointed, for rain-showers fell heavily from the +cloud, bringing down with them the dust and ashes, which covered the +unfortunate sight-seers. + +This was what happened during the eruption, and the result after a few +days was that the cone was a little higher, with a fresh layer of rough +slaggy scoriae on its slopes, and that on the side of the mountain behind +the Hermitage a new lava stream was added to the many which have flowed +there of late years. What then can we learn from this stream about the +materials which come up out of the depths of the earth, and of the +manner in which volcanic rocks are formed? + +The lava as I saw it when coming first out of the newly-opened crater +is, as I have said, like white-hot iron slag, but very soon the top +becomes black and solid, a hard cindery mass full of holes and cavities +with rough edges, caused by the steam and sulphur and other gases +breaking through it.[1] In fact, there are so many holes and bubbles in +it that it is very light and floats on the top of the heavier lava +below, falling over it on to the mountain-side when it comes to the end +of the stream. Still, however, the great mass moves on, so that the +stream slides over these fallen clinkers or scoriae. Thus after an +eruption a new flow consists of three layers; at the top the cooled and +broken crust of clinkers, then the more solid lava, which often remains +hot for years, and lastly another cindery layer beneath, formed of the +scoriae which have fallen from above (see Fig. 40). + + [1] For the cindery nature of the surface of such a stream see the + initial letter of this chapter. + +[Illustration: Fig. 40. + +Section of a lava-flow. (J. Geikie.) + +1, Slaggy crust, formed chiefly of scoriae of a glassy nature. 2, Middle +portion where crystals form. 3, Slaggy crust which has slipped down and +been covered by the flow.] + +You would be surprised to see how quickly the top hardens, so that you +can actually walk across a stream of lava a day or two after it comes +out from the mountain. But you must not stand still or your shoes would +soon be burnt, and if you break the crust with a stick you will at once +see the red-hot lava below; while after a few days the cavities become +filled with crystals of common salt, sulphur or soda, as the vapour and +gases escape. + +Then as time goes on the harder minerals gradually crystallise out of +the melted mass, and iron-pyrites, copper-sulphate, and numerous other +forms of crystal appear in the lower part of the stream. In the clinkers +above, where the cooling goes on very rapidly, the lavas formed are +semi-transparent and look much like common bottle-glass. In fact, if you +take this piece of obsidian or volcanic glass in your hand, you might +think that it had come out of an ordinary glass manufactory and had +nothing remarkable in it. + +[Illustration: Fig. 41. + +A slice of volcanic glass showing the lines of crystallites and +microliths which are the beginnings of crystals.[1] (J. Geikie.)] + + [1] This arrangement in lines is called _fluidal structure_ in lava. + +But the microscope tells another tale. I have put a thin slice under the +first microscope, and this diagram (Fig. 41) shows what you will see. +Nothing, you say, but a few black specks and some tiny dark rods. True, +but these specks and rods are the first beginnings of crystals forming +out of the ground-mass of glassy lava as it cools down. They are not +real crystals, but the first step toward them, and by a careful +examination of glassy lavas which have cooled at different rates, they +have been seen under the microscope in all stages of growth, gradually +building up different crystalline forms. When we remember how rapidly +the top of many glassy lavas cool down we can understand that they have +often only time to grow very small. + +[Illustration: Fig. 42. + +A slice of volcanic glass under the microscope, showing well-developed +microliths. (After Cohen.)] + +The smaller specks are called _crystallites_, the rods are called +_microliths_.[1] Under the next microscope you can see the microliths +much more distinctly (Fig. 42) and observe that they grow in very +regular shapes. + + [1] _Micros_, little; _lithos_, stone. + +Our first slice, however (Fig. 41), tells us something more of their +history, for the fact that they are arranged in lines shows that they +have grown while the lava was flowing and carrying them along in +streams. You will notice that each one has its greatest length in the +direction of the lines, just as pieces of stick are carried along +lengthways in a river. In the second specimen (Fig. 42) the microliths +are much larger and the stream has evidently not been flowing fast, for +they lie in all directions. + +This is what we find in the upper part of the stream, but if we look at +a piece of underlying lava we find that it is much more coarse-grained, +and the magnifying-glass shows many crystals in it, as well as a number +of microliths. For this lava, covered by the crust above, has remained +very hot for a long time, and the crystals have had time to build +themselves up out of the microliths and crystallites. + +Still there is much glassy groundwork even in these lavas. If we want to +find really stony masses such as porphyry and granite made up entirely +of crystals we must look inside the mountain where the molten rock is +kept intensely hot for long periods, as for example in the fissure _g_, +Fig. 39. + +Such fissures sometimes open out on the surface like the one I saw, and +sometimes only penetrate part of the way through the hill; but in either +case when the lava in them cools down, it forms solid walls called dykes +which help to bind the loose materials of the mountain together. We +cannot, of course, examine these in an active volcano, but there are +many extinct volcanoes which have been worn and washed by the weather +for centuries, so that we can see the inside. The dykes laid bare in the +cliffs of Somma are old fissures filled with molten rock which has +cooled down, and they show us many stony lavas; and Mr. Judd tells us of +one beautiful example of a ruined volcano which composes the whole +island of Mull in the Hebrides, where such dykes can be traced right +back to a centre. This centre must once have been a mass of melted +matter far down in the earth, and as you trace the dykes back deeper and +deeper into it, the rocks grow more and more stony, till at last they +are composed entirely of large crystals closely crowded together +without any glassy matter between them. You know this crystalline +structure well, for we have plenty of blocks of granite scattered about +on Dartmoor, showing that at some time long ago molten matter must have +been at work in the depths under Devonshire. + +We see then that we can trace the melted rock of volcanoes right +back--from the surface of the lava stream which cools quickly at the +top, hurrying the crystallites and microliths along with it--down +through the volcano to the depths of the earth, where the perfect +crystals form slowly and deliberately in the underground lakes of +white-hot rock which are kept in a melted state at an intense heat. + +[Illustration: Fig. 43. + +A piece of Dartmoor Granite, drawn from a specimen.] + +But I promised you that we would have no guesswork here, and you will +perhaps ask how I can be certain what was going on in the depths when +these crystals were formed. A few years ago I could not have answered +you, but now chemists, and especially two eminent French chemists, MM. +Fouque and Levy, have actually _made_ lavas and shown us how it is done +in Nature. + +By using powerful furnaces and bellows they have succeeded in getting +temperatures of all degrees, from a dazzling white heat down to a dull +red, and to keep any temperature they like for a long time, so as to +imitate the state of a mass of melted rock at different depths in the +earth, and in this way they have actually _made_ lavas in their +crucibles. For example, there is a certain whitish rock common in +Vesuvius called _leucotephrite_,[1] which is made up chiefly of crystals +of the minerals called leucite, Labrador felspar, and augite. This they +proposed to make artificially, so they took proper quantities of silica, +alumina, oxide of iron, lime, potash, and soda, and putting them in a +crucible, melted them by keeping them at a white heat. Then they lowered +the temperature to an orange-heat, that is a heat sufficient to melt +steel. They kept this heat for forty-eight hours, after which they took +out some of the mixture and, letting it cool, examined a slice under the +microscope. Within it they found crystals of _leucite_ already formed, +showing that these are the first to grow while the melted rock is still +intensely hot. The rest of the mixture they kept red-hot, or at the +melting-point of copper, for another forty-eight hours, and when they +took it out and examined it they found that the whole of it had been +transformed into microliths of the two other forms of crystals, Labrador +felspar and augite, except some small eight-sided crystals of magnetite +and picotite which are also found in the natural rock. + + [1] _Leucos_, white; _tephra_, ashes. + +There is no need for you to remember all these names. What I do want you +to remember is, that, at the different temperatures, the right crystals +and beginnings of crystals grew up to form the rock which is found in +Vesuvius. And what is still more interesting, they grew exactly to the +same stages as in the natural rock, which is composed of _crystals_ of +leucite and _microliths_ of the two other minerals. + +This is only one among numerous experiments by which we have learnt how +volcanic rocks are formed and at what heat the crystals of different +substances grow. We are only as yet at the beginning of this new study, +and there is plenty for you boys to do by and by when you grow up. Many +experiments have failed as yet to imitate certain rocks, and it is +remarkable that these are usually rocks of very ancient eruptions, when +_perhaps_ our globe may have been in a different state to what it is +now; but this remains for us to find out. + +Meanwhile I have still another very interesting slide to show you which +tells us something of what is going on below the volcano. Under the +third microscope I have put a slice of volcanic glass (Fig. 44) in which +you will see really large crystals with dark bands curving round them. +These crystals have clearly not been formed in the glass while the lava +was flowing, first because they are too large to have grown up so +rapidly, and secondly because they are broken at the edges in places and +sometimes partly melted. They have evidently come up with the lava as it +flowed out of the mountain, and the dark bands curving round them are +composed of microliths which have been formed in the flow and have swept +round them, as floating straws gather round a block of wood in a stream. + +Such crystals as these are often found in lava streams, and in fact they +make a great difference in the rate at which a stream flows, for a +thoroughly melted lava shoots along at a great pace and often travels +several miles in a very short time; but an imperfectly melted lava full +of crystals creeps slowly along, and often does not travel far from the +crater out of which it flows. + +[Illustration: Fig. 44. + +Slice of volcanic glass under the microscope, showing large included +crystals brought up from inside the volcano in the fluid lava. The dark +bands are lines of microliths formed as the lava cooled. (J. Geikie.)] + +So you see we have proof in this slice of volcanic glass of two separate +periods of crystallisation--the period when the large crystals grew in +the liquid mass under the mountain, and the period when the microliths +were formed after it was poured out above ground. And as we know that +different substances form their crystals at very different temperatures, +it is not surprising that some should be able to take up the material +they require and grow in the underground lakes of melted matter, even +though the rest of the lava was sufficiently fluid to be forced up out +of the mountain. + +And here we must leave our lava stream. The microscope can tell us yet +more, of marvellous tiny cavities inside the crystals, millions in a +single inch, and of other crystals inside these, all of which have their +history; but this would lead us too far. We must be content for the +present with having roughly traced a flow of lava from the depths below, +where large crystals form in subterranean darkness, to the open air +above, where we catch the tiny beginnings of crystals hardened into +glassy lava before they have time to grow further. + +If you will think a little for yourselves about these wonderful +discoveries made with the magic-glass, you will see how many questions +they suggest to us about the minerals which we find buried in the earth +and running through it in veins, and you will want to know something +about the more precious crystals, such as rubies, diamonds, sapphires, +and garnets, and many others which Nature forms far away out of our +sight. All these depend, though indirectly, upon the strange effects of +underground heat, and if you have once formed a picture in your minds of +what must have been going on before that magnificent lava stream crept +down the mountain-side and added its small contribution to the surface +of the earth, you will study eagerly all that comes in your way about +crystals and minerals, and while you ask questions with the spectroscope +about what is going on in the sun and stars millions of miles away, you +will also ask the microscope what it has to tell of the work going on at +depths many miles under your feet. + + + + +CHAPTER VI + +AN HOUR WITH THE SUN + + +[Illustration] + +Before beginning upon the subject of our lecture to-day I want to tell +you the story of a great puzzle which presented itself to me when I was +a very young child. I happened to come across a little book--I can see +it now as though it were yesterday--a small square green book called +_World without End_, which had upon the cover a little gilt picture of a +stile with trees on each side of it. That was all. I do not know what +the book was about, indeed I am almost sure I never opened it or saw it +again, but that stile and the title "World without End" puzzled me +terribly. What was on the other side of the stile? If I could cross over +it and go on and on should I be in a world which had no ending, and what +would be on the other side? But then there could be no other side if it +was a world without any end. I was very young, you must remember, and I +grew confused and bewildered as I imagined myself reaching onwards and +onwards beyond that stile and never, never resting. At last I consulted +my greatest friend, an old man who did the weeding in my father's +garden, and whom I believed to be very wise. He looked at first almost +as bewildered as I was, but at last light dawned upon him. "I tell you +what it is, Master Arthur," said he, "I do not rightly know what happens +when there is no end, but I do know that there is a mighty lot to be +found out in this world, and I'm thinking we had better learn first all +about that, and perhaps it may teach us something which will help us to +understand the other." + +I daresay you will wonder what this anecdote can have to do with a +lecture on the sun--I will tell you. Last night I stood on the balcony +and looked out far and farther away into the star-depths of the midnight +sky, marvelling what could be the history of those countless suns of +which we see ever more and more as we increase the power of our +telescopes, or catch the faint beams of those we cannot see and make +them print their image on the photographic plate. And, as I grew +oppressed at the thought of this never-ending expanse of suns and at my +own littleness, I remembered all at once the little square book of my +childish days with its gilt stile, and my old friend's advice to learn +first all we can of that which lies nearest. + +So to-day, before we travel away to the stars, we had better inquire +what is known about the one star in the heavens which is comparatively +near to us, our own glorious sun, which sends us all our light and heat, +causes all the movements of our atmosphere, draws up the moisture from +the ground to return in refreshing rain, ripens our harvests, awakens +the seeds and sleeping plants into vigorous growth, and in a word +sustains all the energy and life upon our earth. Yet even this star, +which is more than a million times as large as our earth, and bound so +closely to us that a convulsion on its surface sends a thrill right +through our atmosphere, is still so far off that it is only by +questioning the sunbeams it sends to us, that we can know anything about +it. + +You have already learnt[1] a good deal as to the size, the intense heat +and light, and the photographic power of the sun, and also how his white +beams of light are composed of countless coloured rays which we can +separate in a prism. Now let us pass on to the more difficult problem of +the nature of the sun itself, and what we know of the changes and +commotions going on in that blazing globe of light. + + [1] _Fairyland of Science_, Chapter II. + +We will try first what we can see for ourselves. If you take a card and +make a pin-hole in it, you can look through this hole straight at the +sun without injuring your eye, and you will see a round shining disc on +which, perhaps, you may detect a few dark spots. Then if you take your +hand telescopes, which I have shaded by putting a piece of smoked glass +inside the eye-piece, you will find that this shining disc is really a +round globe, and moreover, although the object-glass of your telescopes +measures only two-and-a-half inches across, you will be able to see the +dark spots very distinctly and to observe that they are shaded, having a +deep spot in the centre with a paler shadow round it. + +[Illustration: Fig. 45. + +Face of the sun projected on a sheet of cardboard C. T, Telescope. _f_, +Finder. _og_, Object-glass. _ep_, Eye-piece. S, Screen shutting off the +diffused light from the window.] + +As, however, you cannot all use the telescopes, and those who can will +find it difficult to point them truly on to the sun, we will adopt still +another plan. I will turn the object-glass of my portable telescope full +upon the sun's face, and bringing a large piece of cardboard on an easel +near to the other end, draw it slowly backward till the eye-piece forms +a clear sharp image upon it (see Fig. 45). This you can all see +clearly, especially as I have passed the eye-piece of the telescope +through a large screen _s_, which shuts off the light from the window. + +You have now an exact image of the face of the sun and the few dark +spots which are upon it, and we have brought, as it were, into our room +that great globe of light and heat which sustains all the life and +vigour upon our earth. + +This small image can, however, tell us very little. Let us next see what +photography can show us. The diagram (Fig. 46) shows a photograph of the +sun taken by Mr. Selwyn in October 1860. Let me describe how this is +done. You will remember that there is a point in the telescope tube +where the rays of light form a real image of the object at which the +telescope is pointed (see p. 44). Now an astronomer who wishes to take a +photograph of the sun takes away the eye-piece of his telescope and puts +a photographic plate in the tube exactly at the place where this real +image is formed. He takes care to blacken the frame of the plate and +shuts up this end of the telescope and the plate in a completely dark +box, so that no diffused light from outside can reach it. Then he turns +his telescope upon the sun that it may print its image. + +But the sun's light is so strong that even in a second of time it would +print a great deal too much, and all would be black and confused. To +prevent this he has a strip of metal which slides across the tube of the +telescope in front of the plate, and in the upper part of this strip a +very fine slit is cut. Before he begins, he draws the metal up so that +the slit is outside the tube and the solid portion within, and he +fastens it in this position by a thread drawn through and tied to a bar +outside. Then he turns his telescope on the sun, and as soon as he +wishes to take the photograph he cuts the thread. The metal slides +across the tube with a flash, the slit passing across it and out again +below in the hundredth part of a second, and in that time the sun has +printed through the slit the picture before you. + +[Illustration: Fig. 46. + +Photograph of the face of the sun, taken by Mr. Selwyn, October 1860, +showing spots, faculae, and mottled surface.] + +In it you will observe at least two things not visible on our +card-image. The spots, though in a different position from where we see +them to-day, look much the same, but round them we see also some bright +streaks called _faculae_, or torches, which often appear in any region +where a spot is forming, while the whole face of the sun appears mottled +with bright and darker spaces intermixed. Those of you who have the +telescopes can see this mottling quite distinctly through them if you +look at the sun. The bright points have been called by many names, and +are now generally known as "light granules," as good a name, perhaps, as +any other. + +This is all our photograph can tell us, but the round disc there shown, +which is called the _photosphere_, or light-giving sphere, is by no +means the whole of the sun, though it is all we see daily with the naked +eye. Whenever a total eclipse of the sun takes place--by the dark body +of the moon coming between us and it, so as to shut out the whole of +this disc--a brilliant white halo, called the crown or _corona_, is seen +to extend for many thousands of miles all round the darkened globe. It +varies very much in shape, sometimes forming a kind of irregular square, +sometimes a circle with off-shoots, as in Fig. 47, which shows what +Major Tennant saw in India during the total eclipse of August 18, 1868, +and at other times it shoots out in long pearly white jets and sheets of +light with dark spaces between. On the whole it varies periodically. At +the time of few sun-spots its extensions are equatorial; but when the +sun's face is much covered with spots, they are diagonal, stretching +away from the spot-zones, but not nearly so far. + +[Illustration: Fig. 47. + +Total eclipse of the sun, as drawn by Major Tennant at Guntoor in India, +August 18, 1868, showing corona and the protuberances seen at the +beginning of totality.] + +And besides this corona there are seen very curious flaming projections +on the edge of the sun, which begin to appear as soon as the moon covers +the bright disc. In our diagram (Fig. 47) you see them on the left side +where the moon is just creeping over the limits of the photosphere and +shutting out the strong light of the sun as the eclipse becomes total. A +very little later they are better seen on the other side just before the +bright edge of the sun is uncovered as the moon passes on its way. These +projections in the real sun are of a bright red colour, and they take on +all manners of strange shapes, sometimes looking like ranges of fiery +hills, sometimes like gigantic spikes and scimitars, sometimes even like +branching fiery trees. They were called _prominences_ before their +nature was well understood, and will probably always keep that name. It +would be far better, however, if some other name such as "glowing +clouds" or "red jets" could be used, for there is now no doubt that they +are jets of gases, chiefly hydrogen, constantly playing over the face of +the sun, though only seen when his brighter light is quenched. They have +been found to shoot up 20,000, 80,000, and even as much as 350,000 miles +beyond the edge of the shining disc; and this last means that the flames +were so gigantic that if they had started from our earth they would have +reached beyond the moon. We shall see presently that astronomers are now +able by the help of the spectroscope to see the prominences even when +there is no eclipse, and we know them to be permanent parts of the +bright globe. + +This gives us at last the whole of the sun, so far as we know. There is, +indeed, a strange faint zodiacal light, a kind of pearly glow seen after +sunset or before sunrise extending far beyond the region of the corona; +but we understand so little about this that we cannot be sure that it +actually belongs to the sun. + +And now how shall I best give you an idea of what little we do know +about this great surging monster of light and heat which shines down +upon us? You must give me all your attention, for I want to make the +facts quite clear, that you may take a firm hold upon them. + +Our first step is to question the sunlight which comes to us; and this +we do with the spectroscope. Let me remind you how we read the story of +light through this instrument. Taking in a narrow beam of light through +a fine slit, we pass the beam through a lens to make the rays parallel, +and then throw it upon a prism or row of prisms, so that each set of +waves of coloured light coming through the slit is bent on its own road +and makes an upright image of the slit on any screen or telescope put to +receive it (see Fig. 21, p. 52). Now when the light we examine comes +from a glowing solid, like white-hot iron, or a glowing liquid, or a gas +under such enormous pressure that it behaves like a liquid, then the +images of the slit always overlap each other, so that we see a +continuous unbroken band of colour. However much you spread out the +light you can never break up or separate the spectrum in any part.[1] +But when you send the light, of a glowing gas such as hydrogen through +the spectroscope, or of a substance melted into gas or vapour, such as +sodium or iron vaporised by great heat, then it is a different story. +Such gases give only a certain number of bright lines quite separate +from each other on the dark background, and each kind of gas gives its +own peculiar lines; so that even when several are glowing together there +is no confusion, but when you look at them through the spectroscope you +can detect the presence of each gas by its own lines in the spectrum. + + [1] Two rare earths, Erbia and Didymium, form an exception to this, + but they do not concern us here. + +[Illustration: TABLE OF SPECTRA. Plate I.] + +To make quite sure of this we will close the shutters and put a pinch of +salt in a spirit-flame. Salt is chloride of sodium, and in the flame the +sodium glows with a bright yellow light. Look at this light through your +small direct-vision spectroscopes[1] and you see at once the bright +yellow double-line of sodium (No. 3, Plate I.) start into view across +the faint continuous spectrum given by the spirit-flame. Next I will +show you glowing hydrogen. I have here a glass tube containing hydrogen, +so arranged that by connecting two wires fastened to it with the +induction coil of our electric battery it will soon glow with a bright +red colour. Look at this through your spectroscopes and you will see +three bright lines, one red, one greenish blue, and one indigo blue, +standing out on the dark background (No. 4, Plate I.) + + [1] A direct-vision spectroscope is like a small telescope with + prisms arranged inside the tube. The object-glass end is covered by + two pieces of metal, which slide backwards and forwards by means of + a screw, so that a narrow or broad slit can be opened. + +Think for a moment what a grand power this gives you of reading as in a +book the different gases which are glowing in the sky even billions of +miles away. You would never mistake the lines of hydrogen for the line +of sodium, but when looking at a nebula or any mass of glowing gas you +could say at once "sodium is glowing there," or "that cloud must be +composed of hydrogen." + +Now, opening the shutters, look at the sunlight through your +spectroscopes. Here you have something different from either the +continuous spectrum of solids, or the bright separate lines of gases, +for while you have a bright-coloured band you have also some dark lines +crossing it (No. 2, Plate I.) It is those dark lines which enable us to +guess what is going on in the sun before the light comes to us. In 1859 +Professor Kirchhoff made an experiment which explained those dark lines, +and we will repeat it now. Take a good look at the sunlight spectrum, to +fix the lines in your memory, and then close the shutters again. + +[Illustration: Fig. 48. + +Kirchhoff's experiment, explaining the dark lines in sunlight. + +A, Limelight dispersed through a prism. _s_, Slit through which the beam +of light comes. _l_, Lens bringing it to a focus on the prism _p_. _sp_, +Continuous spectrum thrown on the wall. B, The same light, with the +flame _f_ containing glowing sodium placed in front of it. D, Dark +sodium line appearing in the spectrum.] + +I have here our magic-lantern with its lime-light, in which the solid +lime glows with a white heat, in consequence of the jets of oxygen and +hydrogen burning round it. This was the light Kirchhoff used, and you +know it will give a continuous bright band in the spectroscope. I put a +cap with a narrow slit in it over the lantern tube, so as to get a +narrow beam of light; in front of this I put a lens _l_, and in front of +this again the prism _p_. The slit and the prism act exactly like your +spectroscopes, and you can all see the continuous spectrum on the screen +(_sp_, A, Fig. 48). Next I put a lighted lamp of very weak spirit in +front of the slit, and find that it makes no difference, for whatever +light it gives only strengthens the spectrum. But now notice carefully. +I am going to put a little salt into the flame, and you would expect +that the sodium in it, when turned to glowing vapour, causing it to look +yellow, would strengthen the yellow part of the spectrum and give a +bright line. This is what Kirchhoff expected, but to his intense +surprise he saw as you do now a _dark line_ D start out where the bright +line should have been. + +What can have happened? It is this. The oxyhydrogen light is very hot +indeed, the spirit flame with the sodium is comparatively weak and cool. +So when those special coloured waves of the oxyhydrogen light which +agree with those of the sodium light reached the flame, they spent all +their energy in heating up those waves to their own temperature, and +while all the other coloured rays travelled on and reached the screen, +these waves were stopped or _absorbed_ on the way, and consequently +there was a blank, black space in the spectrum where they should have +been. If I could put a hydrogen flame cooler than the original light in +the road, then there would be three dark lines where the bright hydrogen +lines should be, and so with every other gas. _The cool vapour in front +of the hot light cuts off from the white ray exactly those waves which +it gives out itself when burning._ + +Thus each black line of the sun-spectrum (No. 2, Plate I.), tells us +that some particular ray of sunlight has been absorbed by a cooler +vapour _of its own kind_ somewhere between the sun and us, and it must +be in the sun itself, for when we examine other stars we often find dark +lines in their spectrum different from those in the sun, and this shows +that the missing rays must have been stopped close at home, for if they +were stopped in our atmosphere they would all be alike. + +There are, by the bye, some lines which we know are caused by our +atmosphere, especially when it is full of invisible water vapour, and +these we easily detect, because they show more distinctly when the sun +is low and shines through a thicker layer of air than when he is high up +and shines through less. + +But to return to the sun. In your small spectroscopes you see very few +dark lines, but in larger and more perfect ones they can be counted by +thousands, and can be compared with the bright lines of glowing gases +burnt here on earth. In the spectrum of glowing iron vapour 460 lines +are found to agree with dark lines in the sun-spectrum, and other gases +have nearly as many. Still, though thousands of lines can now be +explained, by matching them with the bright lines of known gases, the +whole secret of sunlight is not yet solved, for the larger number of +lines still remain a riddle to be read. + +We see then that the spectroscope teaches us that the round light-giving +disc or photosphere of the sun consists of a bright and intensely hot +light shining behind a layer of cooler though still very hot vapours, +which form a kind of shell of luminous clouds around it, and in this +shell, or _reversing layer_--as it is often called, because it turns +light to darkness--we have proved that iron, lead, copper, zinc, +aluminum, magnesium, potassium, sodium, carbon, hydrogen, and many other +substances common to our earth, exist in a state of vapour for a depth +of perhaps 1000 miles. + +You will easily understand that when the spectroscope had told so much, +astronomers were eager to learn what it would reveal about the +prominences or red jets seen during eclipses, and they got an answer in +India during that same eclipse of August 1868 which is shown in our +diagram (Fig. 47). Making use of the time during which the prominences +were seen, they turned the telescope upon them with a spectroscope +attached to it, and saw a number of bright lines start out, of which the +chief were the three bright lines of hydrogen, showing that these +curious appearances are really flames of glowing gas. + +In the same year Professor Jannsen and Mr. Lockyer succeeded in seeing +the bright lines of the prominences in full sunlight. This was done in a +very simple way, when once it was discovered to be possible, and though +my apparatus (Fig. 49) is very primitive compared with some now made, it +will serve to explain the method. + +[Illustration: Fig. 49. + +The spectroscope attached to the telescope for the examination of the +sun. (Lockyer.) + +P, Pillar of Telescope. T, Telescope. S, Finder or small telescope for +pointing the telescope in position. _a_, _a_, _b_, Supports fastening +the spectroscope to the telescope. _d_, Collimator or tube carrying the +slit at the end nearest the telescope, and a lens at the other end to +render the rays parallel. _c_, Plate on which the prisms are fixed. _e_, +Small telescope through which the observer examines the spectrum after +the ray has been dispersed in the prisms. _h_, Micrometer for measuring +the relative distance of the lines.] + +When an astronomer wishes to examine the spectrum of any special part of +the sun, he takes off the eye-piece of his telescope and screws the +spectroscope upon the draw-tube. The spectroscope is made exactly like +the large one for ordinary work. The tube _d_ (Fig. 49) carries the slit +at the end nearest the telescope, and this slit must be so placed as to +stand precisely at the principal focus of the lens where the sun's image +is formed (see _i_, _i_, p. 44). This comes to exactly the same thing as +if we could put the slit close against the face of the sun, so as to +show only the small strip which it covers, and by moving it to one part +or another of the image we can see any point that we wish and no other. +The light then passes through the tube _d_ into the round of prisms +standing on the tray _c_, and the observer looking through the small +telescope _e_ sees the spectrum as it emerges from the last prism. In +this way astronomers can examine the spectrum of a spot, or part of a +spot, or of a bright streak, or any other mark on the sun's face. + +Now in looking at the prominences we have seen that the difficulty is +caused by the sunlight, between us and them, overpowering the bright +lines of the gas, nor could we overcome this if it were not for a +difference which exists between the two kinds of light. The more you +disperse or spread out the continuous sun-spectrum the fainter it +becomes, but in spreading out the bright lines of the gas you only send +them farther and farther apart; they themselves remain almost as bright +as ever. So, when the telescope forms an image of the red flame in front +of the slit, though the glowing gas and the sunlight both send rays into +the spectroscope, you have only to use enough prisms and arrange them in +such a way that the sunlight is dispersed into a very long faint +spectrum, and then the bright lines of the flames will stand out bright +and clear. Of course only a small part of the long spectrum can be seen +at once, and the lines must be studied separately. On the other hand, if +you want to compare the strong light of the sun with the bright lines of +the prominences, you place the slit just at the edge of the sun's image +in the telescope, so that half the slit is on the sun's face and half on +the prominence. The prisms then disperse the sunlight between you and +the prominences, while they only lessen the strong light of the sun +itself, which still shows clearly. In this way the two spectra are seen +side by side and the dark and bright lines can be compared accurately +together (see Fig. 50). + +[Illustration: Fig. 50. + +Bright lines of prominences. + +Sun-spectrum with dark lines.] + +Wherever the telescope is turned all round the sun the lines of luminous +gas are seen, showing that they form a complete layer outside the +photosphere, or light-giving mass, of the sun. This layer of luminous +gases is called the _chromosphere_, or coloured sphere. It lies between +the photosphere and the corona, and is supposed to be at least 5000 +miles deep, while, as we have seen, the flames shoot up from it to +fabulous heights. + +The quiet red flames are found to be composed of hydrogen and another +new metal called helium; but lower down, near the sun's edge, other +bright lines are seen, showing that sodium, magnesium, and other metals +are there, and when violent eruptions occur these often surge up and +mingle with the purer gas above. At other times the eruptions below +fling the red flames aloft with marvellous force, as when Professor +Young saw a long low-lying cloud of hydrogen, 100,000 miles long, blown +into shreds and flung up to a height of 200,000 miles, when the +fragments streamed away and vanished in two hours. Yet all these violent +commotions and storms are unseen by us on earth unless we look through +our magic glasses. + +You will wonder no doubt how the spectroscope can show the height and +the shape of the flames. I will explain to you, and I hope to show them +you one day. You must remember that the telescope makes a small real +image of the flame at its focus, just as in one of our earlier +experiments you saw the exact image of the candle-flame upside down on +the paper (see p. 33). The reason why we only see a strip of the flame +in the spectroscope is because the slit is so narrow. But when once the +sunlight was dispersed so as no longer to interfere, Dr. Huggins found +that it is possible to open the slit wide enough to take in the image of +the whole flame, and then, by turning the spectroscope so as to bring +one of the bright hydrogen lines into view, the actual shape of the +prominence is seen, only it will look a different colour, either red, +greenish-blue, or indigo-blue, according to the line chosen. As the +image of the whole sun and its appendages in the telescope is so very +small, you will understand that even a very narrow slit will really take +in a very large prominence several thousand miles in length. Fig 51 +shows a drawing by Mr. Lockyer of a group of flames he observed very +soon after Dr. Huggins suggested the open slit, and these shapes did not +last long, for in another picture he drew ten minutes later their +appearance had already changed. + +[Illustration: Fig. 51. + +Red prominences, as drawn by Mr. Lockyer during the total eclipse of +March 14, 1869.] + +These then are some of the facts revealed to us by our magic glasses. I +scarcely expect you to remember all the details I have given you, but +you will at least understand now how astronomers actually penetrate into +the secrets of the sun by bringing its image into their observatory, as +we brought it to-day on the card-board, and then making it tell its own +tale through the prisms of the spectroscope; and you will retain some +idea of the central light of the sun with its surrounding atmosphere of +cooler gases and its layer of luminous lambent gases playing round it +beyond. + +Of the corona I cannot tell you much, except that it is far more subtle +than anything we have spoken of yet; that it is always strongest when +the sun is most spotted; that it is partly made up of self-luminous +gases whose bright lines we can see, especially an unknown green ray; +while it also shines partly by reflected light from the sun, for we can +trace in it faint dark lines; lastly it fades away into the mysterious +zodiacal light, and so the sun ends in mystery at its outer fringe as it +began at its centre. + +And now at last, having learnt something of the material of the sun, we +can come back to the spots and ask what is known about them. As I have +said, they are not always the same on the sun's face. On the contrary, +they vary very much both in number and size. In some years the sun's +face is quite free from them, at others there are so many that they form +two wide belts on each side of the sun's equator, with a clear space of +about six degrees between. No spots ever appear near the poles. Herr +Schwabe, who watched the sun's face patiently for more than thirty +years, has shown that it is most spotted about every eleven years, then +the spots disappear very quickly and reappear slowly till the full-spot +time comes round again. + +Some spots remain a very short time and then break up and disappear, but +others last for days, weeks, and even months, and when we watch these, +we find that a spot appears to travel slowly across the face of the sun +from east to west and then round the western edge so that it disappears. +It is when it reaches the edge that we can convince ourselves that the +spot is really part of the sun, for there is no space to be seen between +them, the edge and the spot are one, as the last trace of the dark +blotch passes out of sight. In fact, it is not the spot which has +crossed the sun's face, but the sun itself which has turned, like our +earth, upon its axis, carrying the spot round with it. As some spots +remain long enough to reappear, after about twelve or thirteen days, on +the opposite edge, and even pass round two or three times, astronomers +can reckon that the sun takes about twenty-five days and five hours in +performing one revolution. You will wonder why I say only _about_ +twenty-five, but I do so because all spots do not come round in exactly +the same time, those farthest from the equator lag rather more than a +day behind those nearer to it, and this is explained by the layer of +gases in which they are formed, drifting back in higher latitudes as the +sun turns. + +It is by watching a spot as it travels across the sun, that we are able +to observe that the centre partlies deeper in the sun's face than the +outer rim. There are many ways of testing this, and you can try one +yourselves with a telescope if you watch day after day. I will explain +it by a simple experiment. I have here a round lump of stiff dough, in +which I have made a small hollow and blackened the bottom with a drop of +ink. As I turn this round, so that the hollow facing you moves from +right to left, you will see that after it passes the middle of the face, +the hole appears narrower and narrower till it disappears, and if you +observe carefully you will note that the dark centre is the first thing +you lose sight of, while the edges of the cup are still seen, till just +before the spot disappears altogether. But now I will stick a wafer on, +and a pea half into, the dough, marking the centre of each with ink. +Then I turn the ball again. This time you lose sight of the foremost +edge first, and the dark centre is seen almost to the last moment. This +shows that if the spots were either flat marks, or hillocks, on the +sun's face, the dark centre would remain to the last, but as a fact it +disappears before the rim. Father Secchi has tried to measure the depth +of a spot-cavity, and thinks they vary from 1000 to 3000 miles deep. But +there are many difficulties in interpreting the effects of light and +shadow at such an enormous distance, and some astronomers still doubt +whether spots are really depressions. + +For many centuries now the spots have been watched forming and +dispersing, and this is roughly speaking what is seen to happen. When +the sun is fairly clear and there are few spots, these generally form +quietly, several black dots appearing and disappearing with bright +streaks or _faculae_ round their edge, till one grows bigger than the +rest, and forms a large dark nucleus, round which, after a time, a +half-shadow or _penumbra_ is seen and we have a sun-spot complete, with +bright edges, dark shadow, and deep black centre (Fig. 52). This lasts +for a certain time and then it becomes bridged over with light streaks, +the dark spot breaks up and disappears, and last of all the half-shadow +dies away. + +[Illustration: Fig. 52. + +A quiet sun-spot. (Secchi.)] + +But things do not always take place so quietly. When the sun's face is +very troubled and full of spots, the bright _faculae_, which appear with +a spot, seem to heave and wave, and generally several dark centres form +with whirling masses of light round them, while in some of them tongues +of fire appear to leap up from below (Fig. 53). Such spots change +quickly from day to day, even if they remain for a long time, until at +last by degrees the dark centres become less distinct, the half-shadows +disappear, leaving only the bright streaks, which gradually settle down +into luminous points or _light granules_. These light granules are in +fact supposed by astronomers to be the tips of glowing clouds heaving up +everywhere, while the dark spaces between them are cooler currents +passing downwards. + +[Illustration: Fig. 53. + +A tumultuous sun-spot. (Langley.)] + +Below these clouds, no doubt, the great mass of the sun is in a violent +state of heat and commotion, and when from time to time, whether +suddenly or steadily, great upheavals and eruptions take place, bright +flames dart up and luminous clouds gather and swell, so that long +streaks or _faculae_ surge upon the face of the sun. + +Now these hot gases rising up thus on all sides would leave room below +for cooler gases to pour down from above, and these, as we know, would +cut off, or absorb, much of the light coming from the body of the sun, +so that the centre, where the down current was the strongest, would +appear black even though some light would pass through. This is the best +explanation we have as yet of the formation of a sun-spot, and many +facts shown in the spectroscope help to confirm it, as for example the +thickening of the dark lines of the spectrum when the slit is placed +over the centre of a spot, and the flashing out of bright lines when an +uprush of streaks occurs either across the spots or round it. + +And now, before you go, I must tell you of one of these wonderful +uprushes, which sent such a thrill through our own atmosphere, as to +tell us very plainly the power which the sun has over our globe. The +year 1859 was remarkable for sun-spots, and on September 1, when two +astronomers many miles apart were examining them, they both saw, all at +once, a sudden cloud of light far brighter than the general surface of +the sun burst out in the midst of a group of spots. The outburst began +at eight minutes past eleven in the forenoon, and in five minutes it was +gone again, but in that time it had swept across a space of 35,000 miles +on the sun! Now both before and after this violent outburst took place +a magnetic storm raged all round the earth, brilliant auroras were seen +in all parts of the world, sparks flashed from the telegraph wires, and +the telegraphic signalmen at Washington and Philadelphia received severe +electric shocks. Messages were interrupted, for the storm took +possession of the wires and sent messages of its own, the magnetic +needles darting to and fro as though seized with madness. At the +very instant when the bright outburst was seen in the sun, the +self-registering instruments at Kew marked how three needles jerked all +at once wildly aside; and the following night the skies were lit up with +wondrous lights as the storm of electric agitation played round the +earth. + +We are so accustomed to the steady glow of sunshine pouring down upon us +that we pay very little heed to daylight, though I hope none of us are +quite so ignorant as the man who praised the moon above the sun, because +it shone in the dark night, whereas the sun came in the daytime when +there was light enough already! Yet probably many of us do not actually +realise how close are the links which bind us to our brilliant star as +he carries us along with him through space. It is only when an unusual +outburst occurs, such as I have just described, that we feel how every +thrill which passes through our atmosphere, through the life-current of +every plant, and through the fibre and nerve of every animal has some +relation to the huge source of light, heat, electricity, and magnetism +at which we are now gazing across a space of more than 93,000,000 miles. +Yet it is well to remember that the sudden storm and the violent +eruption are the exceptional occurrences, and that their use to us as +students is chiefly to lead us to understand the steady and constant +thrill which, never ceasing, never faltering, fulfils the great purpose +of the unseen Lawgiver in sustaining all movement and life in our little +world. + + + + +CHAPTER VII + +AN EVENING AMONG THE STARS + + +[Illustration] + +"Do you love the stars?" asked the magician of his lads, as they crowded +round him on the college green, one evening in March, to look through +his portable telescope. + +"Have you ever sat at the window on a clear frosty night, or in the +garden in summer, and looked up at those wondrous lights in the sky, +pondering what they are, and what purpose they serve?" + +I will confess to you that when I lived in London I did not think much +about the stars, for in the streets very few can be seen at a time even +on a clear night; and during the long evenings in summer, when town +people visit the country, you must stay up late to see a brilliant +display of starlight. It is when driving or walking across country on a +winter's evening week after week, and looking all round the sky, that +the glorious suns of heaven force you to take notice of them; and Orion +becomes a companion with his seven brilliant stars and his magnificent +nebula, which appears as a small pale blue patch, to eyes accustomed to +look for it, when the night is very bright and clear. It is then that +Charles's Wain becomes quite a study in all its different positions, its +horses now careering upwards, now plunging downwards, while the waggon, +whether upwards or downwards, points ever true, by the two stars of its +tail-board, to the steadfast pole-star. + +It is on such nights as these that, looking southward from Orion, we +recognise the dog-star Sirius, bright long before other stars have +conquered the twilight, and feast our eye upon his glorious white beams; +and then, turning northwards, are startled by the soft lustrous sheen of +Vega just appearing above the horizon. + +But stop, I must remember that I have not yet introduced you to these +groups of stars; and moreover that, though we shall find them now in the +positions I mention, yet if you look for them a few hours later +to-night, or at the same hour later in the year, you will not find them +in the same places in the sky. For as our earth turns daily on its axis, +the stars _appear_ to alter their position hour by hour, and in the same +way as we travel yearly on our journey round the sun, they _appear_ to +move in the sky month by month. Yet with a little practice it is easy to +recognise the principal stars, for, as it is our movement and not theirs +which makes us see them in different parts of the sky, they always +remain in the same position with regard to each other. In a very short +time, with the help of such a book as Proctor's _Star Atlas_; you could +pick out all the chief constellations and most conspicuous stars for +yourselves. + +One of the best ways is to take note of the stars each night as they +creep out one by one after sunset. If you take your place at the window +to-morrow night as the twilight fades away, you will see them gradually +appear, now in one part, now in another of the sky, as + + "One by one each little star + Sits on its golden throne." + +The first to appear will be Sirius or the dog-star (see Fig. 54), that +pure white star which you can observe now rather low down to the south, +and which belongs to the constellation _Canis Major_. As Sirius is one +of the most brilliant stars in the sky, he can be seen very soon after +the sun is gone at this time of year. If, however, you had any doubt as +to what star he was, you would not doubt long, for in a little while two +beautiful stars start into view above him more to the west, and between +them three smaller ones in a close row, forming the cross in the +constellation of Orion, which is always very easy to recognise. Now the +three stars of Orion's belt which make the short piece of the cross +always point to Sirius, while Betelgeux in his right shoulder, and Rigel +in his left foot (see Figs. 54 and 55), complete the long piece, and +these all show very early in the twilight. You would have to wait longer +for the other two leading stars, Bellatrix in the right shoulder and +[Greek: k] Orionis in the right leg, for these stars are feebler and +only seen when the light has faded quite away. + +[Illustration: Fig. 54. + +Some of the constellations seen when looking south in March from six to +nine o'clock.] + +By that time you would see that there are an immense number of stars in +Orion visible even to the naked eye, besides the veil of misty, tiny +stars called the "Milky Way" which passes over his arm and club. Yet the +figure of the huntsman is very difficult to trace, and the seven bright +stars, the five of the cross and those in the left arm and knee, are all +you need remember. + +No! not altogether all, for on a bright clear night like this you can +detect a faint greenish blue patch (N, Fig. 54) just below the belt, and +having a bright star in the centre. This is called the "Great Nebula" or +mist of Orion (see Frontispiece). With your telescopes it looks very +small indeed, for only the central and brightest part is seen. Really, +however, it is so widespread that our whole solar system is as nothing +compared to it. But even your telescopes will show, somewhere near the +centre, what appears to be a bright and very beautiful star (see Fig. +55) surrounded by a darker space than the rest of the nebula, while in +my telescope you will see many stars scattered over the mist. + +[Illustration: Fig. 55. + +Chief stars of Orion, with Aldebaran. (After Proctor.)] + +Now first let me tell you that these last stars do not, so far as we +know, lie _in_ the nebula, but are scattered about in the heavens +between us and it, perhaps millions of miles nearer our earth. But with +the bright star in the centre it is different, for the spectroscope +tells us that the mist passes _over_ it, so that it is either behind or +in the nebula. Moreover, this star is very interesting, for it is not +really one star, but six arranged in a group (see Fig. 56). You can see +four distinctly through my telescope, forming a trapezium or four-sided +figure, and more powerful instruments show two smaller ones. So [Greek: +th] Orionis, or the Trapezium of Orion, is a multiple star, probably +lying in the midst of the nebula. + +[Illustration: Fig. 56. + +The trapezium, [Greek: th] Orionis, in the nebula of Orion. (Herschel.)] + +The next question is, What is the mist itself composed of? For a long +time telescopes could give us no answer. At last one night Lord Rosse, +looking through his giant telescope at the densest part of the nebula, +saw myriads of minute stars which had never been seen before. "Then," +you will say, "it is after all only a cluster of stars too small for our +telescopes to distinguish." Wait a bit; it is always dangerous to draw +hasty conclusions from single observations. What Lord Rosse said was +true as to that particular part of the nebula, but not the whole truth +even there, and not at all true of other parts, as the spectroscope +tells us. + +For though the light of nebulae, or luminous mists, is so faint that a +spectrum can only be got by most delicate operations, yet Dr. Huggins +has succeeded in examining several. Among these is the nebula of Orion, +and we now know that when the light of the mist is spread out it gives, +not a continuous band of colour such as would be given by stars, but +_faint coloured lines_ on a dark ground (see Fig. 57). Such lines as +these we have already learnt are always given by gases, and the +particular bright lines thrown by Orion's nebula answer to those given +by nitrogen and hydrogen, and some other unknown gases. So we learn at +last that the true mist of the nebula is formed of glowing gas, while +parts have probably a great number of minute stars in them. + +[Illustration: Fig. 57. + +Nebula-spectrum. + +Sun-spectrum. + +Spectrum of Orion's Nebula, showing bright lines, with sun-spectrum +below for comparison.] + +Till within a very short time ago only those people who had access to +very powerful telescopes could see the real appearance of Orion, for +drawings made of it were necessarily very imperfect; but now that +telescopes have been made expressly for carrying photographic +appliances, even these faint mists print their own image for us. In 1880 +Professor Draper of America photographed the nebula of Orion, in March +1881 Mr. Common got a still better effect, and last year Mr. Isaac +Roberts succeeded in taking the most perfect and beautiful photograph[1] +yet obtained, in which the true beauty of this wonderful mist stands out +clearly. I have marked on the edge of our copy two points [Greek: th] +and [Greek: th]', and if you follow out straight lines from these points +till they meet, you will arrive at the spot where the multiple star +lies. It cannot, however, be seen here, because the plate was exposed +for three hours and a half, and after a time the mist prints itself so +densely as to smother the light of the stars. Look well at this +photograph when you go indoors and fix it on your memory, and then on +clear nights accustom your eye to find the nebula below the three stars +of the belt, for it tells a wonderful story. + + [1] Reproduced in the Frontispiece with Mr. Roberts's kind permission. + The star-halo at the top of the plate is caused by diffraction of + light in the telescope, and comes only from an ordinary star. + +More than a hundred years ago the great German philosopher Kant +suggested that our sun, our earth, and all the heavenly bodies might +have begun as gases, and the astronomer Laplace taught this as the most +likely history of their formation. After a few years, however, when +powerful telescopes showed that many of the nebulae were only clusters of +very minute stars, astronomers thought that Laplace's teaching had been +wrong. But now the spectroscope has revealed to us glowing gas actually +filling large spaces in the sky, and every year accurate observations +and experiments tell us more and more about these marvellous distant +mists. Some day, though perhaps not while you or I are here to know it, +Orion's nebula, with its glowing gas and minute star-dust, may give some +clue to the early history of the heavenly bodies; and for this reason I +wish you to recognise and ponder over it, as I have often done, when it +shines down on the rugged moor in the stillness of a clear frosty +winter's night. + +But we must pass on for, while I have been talking, the whole sky has +become bespangled with hundreds of stars. That glorious one to the west, +which you can find by following (Fig. 54) a curved line upwards from +Betelgeux, is the beautiful red star Aldebaran or the hindmost; so +called by the Arabs, because he drives before him that well-known +cluster, the Pleiades, which we reach by continuing the curve westwards +and upwards. Stop to look at this cluster through your telescopes, for +it will delight you; even with the naked eye you can count from six to +ten stars in it, and an opera-glass will show about thirty, though they +are so scattered you will have to move the glass about to find them. Yet +though my telescope shows a great many more, you cannot even count all +the chief ones through it, for in powerful telescopes more than 600 +stars have been seen in the single cluster! while a photograph taken by +Mr. Roberts shows also four lovely patches of nebula. + +And now from the Pleiades let us pass on directly overhead to the +beautiful star Capella, which once was red but now is blue, and drop +down gently to the south-east, where Castor and Pollux, the two most +prominent stars in the constellation "Gemini" or the twins, show +brilliantly against the black sky. Pause here a moment, for I want to +tell you something about Castor, the one nearest to Capella. If you look +at Castor through your telescopes, some of you may possibly guess that +it is really two stars, but you will have to look through mine to see it +clearly. These two stars have been watched carefully for many years, and +there is now no doubt that one of them is moving slowly round the other. +Such stars as these are called "binary," to distinguish them from stars +that merely _appear_ double because they stand nearly in a line one +behind the other in the heavens, although they may be millions of miles +apart. But "binary" stars are actually moving in one system, and revolve +round each other as our earth moves round the sun. + +I wonder if it strikes you what a grand discovery this is? You will +remember that it is gravitation which keeps the moon held to the earth +so that it moves round in a circle, and which keeps the earth and other +planets moving round the sun. But till these binary stars were +discovered we had no means of guessing that this law had any force +beyond our own solar system. Now, however, we learn that the same law +and order which reigns in our small group of planets is in action +billions of miles away among distant suns, so that they are held +together and move round each other as our earth moves round our sun. I +will repeat to you what Sir R. Ball, the Astronomer-Royal of Ireland, +says about this, for his words have remained in my mind ever since I +read them, and I should like them to linger in yours till you are old +enough to feel their force and grandeur. "This discovery," he writes, +"gave us knowledge we could have gained from no other source. From the +binary stars came a whisper across the vast abyss of space. That whisper +told us that the law of gravitation is not peculiar to the solar system. +It gives us grounds for believing that it is obeyed throughout the +length, the breadth, the depth, and the height of the entire +universe."[1] + + [1] _The Story of the Heavens._ + +And now, leaving Castor and going round to the east, we pass through the +constellation Leo or the Lion, and I want you particularly to notice six +stars in the shape of a sickle, which form the front part of the lion, +the brightest, called Regulus, being the end of the handle.[1] This +sickle is very interesting, because it marks the part of the heavens +from which the brilliant shower of November meteors radiates once in +thirty-three years. This is, however, too long a story to be told +to-night, so we will pass through Leo, and turning northwards, look high +up in the north-east (Fig. 58), where "Charles's Wain" stretches far +across the sky. I need not point this out to you, for every country lad +knows and delights in it. You could not have seen it in the twilight +when Sirius first shone out, for these stars are not so powerful as he +is. But they come out very soon after him, and when once fairly bright, +the four stars which form the waggon, wider at the top than at the +bottom, can never be mistaken, and the three stars in front, the last +bending below the others, are just in the right position for the horses. +For this reason I prefer the country people's name of Charles's Wain or +Waggon to that of the "Plough," which astronomers generally give to +these seven stars. They really form part of an enormous constellation +called the "Great Bear" (Fig. 59), but, as in the case of Orion, it is +very difficult to make out the whole of Bruin in the sky. + + [1] In Fig. 54 the sickle alone comes within the picture. + +[Illustration: Fig. 58. + +Some of the constellations seen when looking north in March from six to +nine o'clock.] + +[Illustration: Fig. 59. + +The Great Bear, showing the position of Charles's Wain, and also the +small binary star [Greek: x] in the hind foot, whose period has been +determined.] + +Now, although most people know Charles's Wain when they see it, we may +still learn a good deal about it. Look carefully at the second star from +the waggon and you will see another star close to it, called by country +people "Jack by the second horse," and by astronomers "Alcor." Even in +your small telescopes you can see that Jack or Alcor is not so close as +he appears to the naked eye, but a long way off from the horse, while in +my telescope you will find this second horse (called Mizar) split up +into two stars, one a brilliant white and the other a pale emerald +green. We do not know whether these two form a binary, for they have not +yet been observed to move round each other. + +Take care in looking that you do not confuse the stars one with another, +for you must remember that your telescope makes objects appear upside +down, and Alcor will therefore appear in it _below_ the two stars +forming the horse. + +But though we do not know whether Mizar is binary, there is a little +star a long way below the waggon, in the left hind paw of the Great Bear +([Greek: x], Figs. 58 and 59), which has taught us a great deal, for it +is composed of two stars, one white and the other grey, which move right +round each other once in sixty years, so that astronomers have observed +more than one revolution since powerful telescopes were invented. You +will have to look in my telescope to see the two stars divided, but you +can make an interesting observation for yourselves by comparing the +light of this binary star with the light of Castor, for Castor is such +an immense distance from us that his light takes more than a hundred +years to reach us, while the light of this smaller star comes in +sixty-one years, yet see how incomparably brighter Castor is of the two. +This proves that brilliant stars are not always the nearest, but that a +near star may be small and faint and a far-off one large and bright. + +[Illustration: Fig. 60. + +The seven stars of Charles's Wain, showing the directions in which they +are travelling. (After Proctor.)] + +There is another very interesting fact known to us about Charles's Wain +which I should like you to remember when you look at it. This is that +the seven stars are travelling onwards in the sky, and not all in the +same direction. It was already suspected centuries ago that, besides the +_apparent_ motion of all the stars in the heavens caused by our own +movements, they have each also a _real_ motion and are travelling in +space, though they are so inconceivably far off that we do not notice +it. It has now been proved, by very accurate observations with powerful +instruments, that three of the stars forming the waggon and the two +horses nearest to it, together with Jack, are drifting forwards (see +Fig. 60), while the top star of the tailboard of the waggon and the +leader of the horses are drifting the other way. Thus, thousands of +years hence Charles's Wain will most likely have quite altered its +shape, though so very slowly that each generation will think it is +unchanged. + +One more experiment with Charles's Wain, before we leave it, will help +you to imagine the endless millions of stars which fill the universe. +Look up at the waggon and try to count how many stars you can see inside +it with the naked eye. You may, if your eye is keen, be able to count +twelve. Now take an opera-glass and the twelve become two hundred. With +your telescopes they will increase again in number. In my telescope +upstairs the two hundred become hundreds, while in one of the giant +telescopes, such as Lord Rosse's in Ireland, or the great telescope at +Washington in the United States, thousands of stars are brought into +view within that four-sided space! + +Now this part of the sky is not fuller of stars than many others; yet at +first, looking up as any one might on a clear evening, we thought only +twelve were there. Cast your eyes all round the heavens. On a clear +night like this you may perhaps, with the naked eye, have in view about +3000 stars; then consider that a powerful telescope can multiply these +by thousands upon thousands, so that we can reckon about 20,000,000 +where you see only 3000. If you add to these the stars that rise later +at night, and those of the southern hemisphere which never rise in our +latitude, you would have in all about 50,000,000 stars, which we are +able to see from our tiny world through our most powerful telescopes. + +But we can go farther yet. When our telescopes fail, we turn to our +other magic seer, the photographic camera, and trapping rays of light +from stars invisible in the most powerful telescope, make them print +their image on the photographic plate, and at once our numbers are so +enormously increased that if we could photograph the whole of the +heavens as visible from our earth, we should have impressions of at +least 170,000,000 stars! + +These numbers are so difficult to grasp that we had better pass on to +something easier, and our next step brings us to the one star in the +heavens which never appears to move, as our world turns. To find it we +have only to draw a line upwards through the two stars in the tailboard +of the waggon and on into space. Indeed these two stars are called "the +Pointers," because a line prolonged onwards from them will, with a very +slight curve, bring us to the "Pole-star" (see Fig. 58). This star, +though not one of the largest, is important, because it is very near +that spot in the sky towards which the North Pole of our earth points. +The consequence is, that though all the other stars appear to move in a +circle round the heavens, and to be in different places at different +seasons, this star remains always in the same place, only appearing to +describe a very tiny circle in the sky round the exact spot to which our +North Pole points. + +Month after month and year after year it shines exactly over that +thatched cottage yonder, which you see now immediately below it; and +wherever you are in the northern hemisphere, if you once note a certain +tree, or chimney, or steeple which points upwards to the Pole-star, it +will guide you to it at any hour on any night of the year, though the +other constellations will be now on one side, now on the other side of +it. + +The Pole-star is really the front horse of a small imitation of +Charles's Wain, which, however, has never been called by any special +name, but only part of the "Little Bear." Those two hind stars of the +tiny waggon, which are so much the brightest, are called the "Guards," +because they appear to move in a circle round the Pole-star night after +night and year after year like sentries. + +[Illustration: Fig. 61. + +The constellation of Cassiopeia, and the heavenly bodies which can be +found by means of it.[1]] + + [1] For Almach see Fig. 58, it has been accidentally omitted from this + figure. + +Opposite to them, on the farther side of the Pole-star, is a well-marked +constellation, a widespread W written in the sky by five large stars; +the second V of the W has rather a longer point than the first, and as +we see it now the letter is almost upside down (see Fig. 58). + +These are the five brightest stars in the constellation Cassiopeia, with +a sixth not quite so bright in the third stroke of the W. You can never +miss them when you have once seen them, even though they lie in the +midst of a dense layer of the stars of the Milky Way, and if you have +any difficulty at first, you have only to look as far on the one side of +the Pole-star as the top hind star of Charles's Wain is on the other, +and you must find them. I want to use them to-night chiefly as guides to +find two remarkable objects which I hope you will look at again and +again. The first is a small round misty patch not easy to see, but which +you will find by following out the _second_ stroke of the first V of the +W. Beginning at the top, and following the line to the point of the V, +continue on across the sky, and then search with your telescope till you +catch a glimpse of this faint mist (_c_, Fig. 58; star-cluster, Fig. +61). You will see at once that it is sparkling all over with stars, for +in fact you have actually before you in that tiny cluster more stars +than you can see with the naked eye all over the heavens! Think for a +moment what this means. One faint misty spot in the constellation +Perseus, which we should have passed over unheeded without a telescope, +proves to be a group of more than 3000 suns! + +The second object you will find more easily, for it is larger and +brighter, and appears as a faint dull spot to the naked eye. Going back +to Cassiopeia, follow out the _second_ V in the W from the top to the +point of the V and onwards till your eye rests upon this misty cloud, +which is called the Great Nebula of Andromeda, and has sometimes been +mistaken for a comet (Figs. 58 and 61). You will, however, be +disappointed when you look through the telescope, for it will still only +appear a mist, and you will be able to make nothing of it, except that +instead of being of an irregular shape like Orion, it is elliptical; and +in a powerful telescope two dark rifts can be seen separating the +streams of nebulous matter. These rifts are now shown in a photograph +taken by Mr. Roberts, 1st October 1888, to be two vast dusky rings lying +between the spiral stream of light, which winds in an ellipse till it +ends in a small nucleus at the centre. + +Ah! you will say, this must be a cloud of gas like Orion's nebula, only +winding round and round. No! the spectroscope steps in here and tells us +that the light shows something very much like a continuous spectrum, but +not as long as it ought to be at the red end. Now, since gases give only +bright lines, this nebula cannot be entirely gaseous. Then it must be +made of stars too far off to see? If so, it is very strange that though +it is so dense and bright in some parts, and so spread out and clear in +others, the most powerful telescopes cannot break it up into stars. In +fact, the composition of the great nebula of Andromeda is still a +mystery, and remains for one of you boys to study when he has become a +great astronomer. + +Still one more strange star we will notice before we leave this part of +the heavens. You will find it, or at least go very near it, by +continuing northwards the line you drew from Cassiopeia to the Star +Cluster (_c_, Fig. 58), and as it is a bright star, you will not miss +it. That is to say, it is bright to-night and will remain so till +to-morrow night, but if you come to me about nine o'clock to-morrow +evening I will show you that it is growing dim, and if we had patience +to watch through the night we should find, three or four hours later +still, that it looks like one of the smaller stars. Then it will begin +to brighten again, and in four hours more will be as bright as at first. +It will remain so for nearly three days, or, to speak accurately, 2 +days, 20 hours, 48 minutes, and 55 seconds, and then will begin to grow +dull again. This star is called Algol the Variable. There are several +such stars in the heavens, and we do not know why they vary, unless +perhaps some dark globe passes round them, cutting off part of their +light for a time. + +And now, if your eyes are not weary, let us go back to the Pole-star and +draw a line from it straight down the horizon due north. Shortly before +we arrive there you will see a very brilliant bluish-white star a little +to the east of this line. This is Vega, one of the brightest stars in +the heavens except Sirius. It had not risen in the earlier part of the +evening, but now it is well up and will appear to go on, steadily +mounting as it circles round the Pole-star, till at four o'clock +to-morrow morning it will be right overhead towards the south. + +But beautiful as Vega is, a still more interesting star lies close to it +(see Fig. 58). This small star, called [Greek: e] Lyrae by astronomers, +looks a little longer in one direction than in the other, and even with +the naked eye some people can see a division in the middle dividing it +into two stars. Your telescopes will show them easily, and a powerful +telescope tells a wonderful story, for it reveals that each of these two +stars is again composed of two stars, so that [Greek: e] Lyrae (Fig. 62) +is really a double-double star. There is no doubt that each pair is a +binary star, that is, the two stars move round each other very slowly, +and possibly both pairs may also revolve round a common centre. There +are at least 10,000 double stars in the heavens; though, as we have +seen, they are not all binary. The list of binary stars, however, +increases every year as they are carefully examined, and probably about +one star in three over the whole sky is made up of more than one sun. + +[Illustration: Fig. 62. + +[Greek: e] Lyrae. A double-binary star. Each couple revolves, and the +couples probably also revolve round each other. (After Chambers.)] + +Let us turn the telescope for a short time upon a few of the double +stars and we shall have a great treat, for one of the most interesting +facts about them is that both stars are rarely of the same colour. It +seems strange at first to speak of stars as coloured, but they do not by +any means all give out the same kind of light. Our sun is yellow, and so +are the Pole-star and Pollux; but Sirius, Vega, and Regulus are +dazzling white or bluish-white, Arcturus is a yellowish-white, +Aldebaran is a bright yellow-red, Betelgeux a deep orange-red, as you +may see now in the telescope, for he is full in view; while Antares, a +star in the constellation of the Scorpion, which at this time of year +cannot be seen till four in the morning, is an intense ruby red. + +[Illustration: _Plate II._] + +COLOURED DOUBLE STARS. + +[Illustration: [Greek: g] _Andromedae_.] + +[Illustration: [Greek: e] _Booetis_.] + +[Illustration: [Greek: d] _Geminorum_.] + +[Illustration: [Greek: a] _Herculis_.] + +[Illustration: [Greek: b] _Cygni_.] + +[Illustration: [Greek: e] _Cassiopeiae_.] + +It appears to be almost a rule with double stars to be of two colours. +Look up at Almach ([Greek: g] Andromedae), a bright star standing next to +Algol the Variable in the sweep of four bright stars behind Cassiopeia +(see Fig. 58). Even to the naked eye he appears to flash in a strange +way, and in the telescope he appears as two lovely stars, one a deep +orange and the other a pale green, while in powerful telescopes the +green one splits again into two (Plate II.) Then again, [Greek: e] +Cassiopeae, the sixth star lying between the two large ones in the second +V of Cassiopeia, divides into a yellow star and a small rich purple one, +and [Greek: d] Geminorum, a bright star not far from Pollux in the +constellation Gemini, is composed of a large green star and a small +purple one. Another very famous double star ([Greek: b] Cygni), which +rises only a little later in the evening, lies below Vega a little to +the left. It is composed of two lovely stars; one an orange yellow and +the other blue; while [Greek: e] Booetis, just visible above the horizon, +is composed of a large yellow star and a very small green one.[1] + + [1] The plate of coloured stars has been most kindly drawn to scale + and coloured for me by Mr. Arthur Cottam, F.R.A.S. + +There are many other stars of two colours even among the few +constellations we have picked out to-night, as, for example, the star +at the top of the tailboard of Charles's Waggon and the second horse +Mizar. Rigel in Orion, and the two outer stars of the belt, [Greek: a] +Herculis, which will rise later in the evening, and the beautiful triple +star ([Greek: z] Cancer) near the Beehive (see Fig. 54), are all +composed of two or more stars of different colours. + +Why do these suns give out such beautiful coloured light? The telescope +cannot tell us, but the spectroscope again reveals the secrets so long +hidden from us. By a series of very delicate experiments, Dr. Huggins +has shown that the light of all stars is sifted before it comes to us, +just as the light of our sun is; and those rays which are least cut off +play most strongly on our eyes, and give the colour to the star. The +question is a difficult one but I will try to give you some idea of it, +that you may form some picture in your mind of what happens. + +We learnt in our last lecture (p. 131) that the light from our sun +passes through the great atmosphere of vapours surrounding him before it +goes out into space, and that many rays are in this way cut off; so that +when we spread out his light in a long spectrum there are dark lines or +spaces where no light falls.[1] Now in sunlight these dark lines are +scattered pretty evenly over the spectrum, so that about as much light +is cut off in one part as in another, and no one colour is stronger than +the rest. + + [1] See No. 1 in Table of Spectra, Plate I. + +Dr. Huggins found, however, that in coloured stars the dark spaces are +often crowded into particular parts of the long band of colour forming +the spectrum; showing that many of those light-rays have been cut off +in the atmosphere round the star, and thus their particular colours are +dimmed, leaving the other colour or colours more vivid. In red stars, +for example, the yellow, blue, and green parts of the spectrum are much +lined while the red end is strong and clear. With blue stars it is just +the opposite, and the violet end is most free from dark lines. So there +are really brilliantly coloured suns shining in the heavens, and in many +cases two or more of these revolve round each other. + +And now I have kept your attention and strained your eyes long enough, +and you have objects to study for many a long evening before you will +learn to see them plainly. You must not expect to find them every night, +for the lightest cloud or the faintest moonlight will hide many of them +from view; and, moreover, though you may learn to use the telescope +fairly, you will often not know how to get a clear view with it. Still, +you may learn a great deal, and before we go in I want to put a thought +into your minds which will make astronomy still more interesting. We +have seen that the stronger our telescopes the more stars, +star-clusters, and nebulae we see, and we cannot doubt that there are +still countless heavenly bodies quite unknown to us. Some years ago +Bessel the astronomer found that Sirius, in its real motion through the +heavens, moves irregularly, travelling sometimes a little more slowly +than at other times, and he suggested that some unseen companion must be +pulling at him. + +Twenty-eight years later, in 1862, two celebrated opticians, father and +son, both named Alvan Clark, were trying a new telescope at Chicago +University, when suddenly the son, who was looking at Sirius, exclaimed, +"Why, father, the star has a companion!" And so it was. The powerful +telescope showed what Bessel had foretold, and proved Sirius to be a +"binary" star--that is, as we have seen, a star which has another moving +round it. + +It has since been proved that this companion is twenty-eight times +farther from Sirius than we are from our sun, and moves round him in +about forty-nine years. It is seven times as heavy as our sun, and yet +gives out so little light that only the keenest telescopes can bring it +into view. + +Now if such a large body as this can give so very faint a light that we +can scarcely see it, though Sirius, which is close to it, shines +brightest of any star in the heavens, how many more bodies must there be +which we shall never see, even among those which give out light, while +how many there are dark like our earth, who can tell? + +Now that we know each of the stars to be a brilliant sun, many of them +far, far brighter than ours, yet so like in their nature and laws, we +can scarcely help speculating whether round these glorious suns, worlds +of some kind may not be moving. If so, and there are people in them, +what a strange effect those double coloured suns must produce with red +daylight one day and blue daylight another! + +Surely, as we look up at the myriads of stars bespangling the sky, and +remember that our star-sun has seven planets moving round it of which +one at least--our own earth--is full of living beings, we must picture +these glorious suns as the centres of unseen systems, so that those +twinkling specks become as suggestive as the faint lights of a great +fleet far out at sea, which tell us of mighty ships, together with +frigates and gunboats, full of living beings, though we cannot see them, +nor even guess what they may be like. How insignificant we feel when we +look upon that starlit sky and remember that the whole of our solar +system would be but a tiny speck of light if seen as far off as we see +the stars! If our little earth and our short life upon it were all we +could boast of we should be mites indeed. + +But our very study to-night lifts us above these and reminds us that +there is a spirit within us which even now can travel beyond the narrow +bounds of our globe, measure the vast distances between us and the +stars, gauge their brightness, estimate their weight, and discern their +movements. As we gaze into the depths of the starlit sky, and travel +onwards and onwards in imagination to those distant stars which +photography alone reveals to us, do not our hearts leap at the thought +of a day which must surely come when, fettered and bound no longer to +earth, this spirit shall wander forth and penetrate some of the mystery +of those mighty suns at which we now gaze in silent awe. + + + + +CHAPTER VIII + +LITTLE BEINGS FROM A MINIATURE OCEAN + + +[Illustration] + +In our last lecture we soared far away into boundless space, and lost +ourselves for a time among seen and unseen suns. In this lecture we will +come back not merely to our little world, nor even to one of the +widespread oceans which cover so much of it, but to one single pool +lying just above the limits of low tide, so that it is only uncovered +for a very short time every day. This pool is to be found in a secluded +bay within an hour's journey by train from this college, and only a few +miles from Torquay. It has no name, so far as I know, nor do many people +visit it, otherwise I should not have kept my little pool so long +undisturbed. As it is, however, for many years past I have had only to +make sure as to the time of low tide, and put myself in the train; and +then, unless the sea was very rough and stormy, I could examine the +little inhabitants of my miniature ocean in peace. + +The pool lies in a deep hollow among a group of rocks and boulders, +close to the entrance of the cove, which can only be entered at low +water; it does not measure more than two feet across, so that you can +step over it, if you take care not to slip on the masses of green and +brown seaweed growing over the rocks on its sides, as I have done many a +time when collecting specimens for our salt-water aquarium. I find now +the only way is to lie flat down on the rock, so that my hands and eyes +are free to observe and handle, and then, bringing my eye down to the +edge of the pool, to lift the seaweeds and let the sunlight enter into +the chinks and crannies. In this way I can catch sight of many a small +being either on the seaweed or the rocky ledges, and even creatures +transparent as glass become visible by the thin outline gleaming in the +sunlight. Then I pluck a piece of seaweed, or chip off a fragment of +rock with a sharp-edged collecting knife, bringing away the specimen +uninjured upon it, and place it carefully in its own separate bottle to +be carried home alive and well. + +Now though this little pool and I are old friends, I find new treasures +in it almost every time I go, for it is almost as full of living things +as the heavens are of stars, and the tide as it comes and goes brings +many a mother there to find a safe home for her little ones, and many a +waif and stray to seek shelter from the troublous life of the open +ocean. + +You will perhaps find it difficult to believe that in this rock-bound +basin there can be millions of living creatures hidden away among the +fine feathery weeds; yet so it is. Not that they are always the same. At +one time it may be the home of myriads of infant crabs, not an eighth of +an inch long, at another of baby sea-urchins only visible to the naked +eye as minute spots in the water, at another of young jelly-fish growing +on their tiny stalks, and splitting off one by one as transparent bells +to float away with the rising tide. Or it may be that the whelk has +chosen this quiet nook to deposit her leathery eggs; or young barnacles, +periwinkles, and limpets are growing up among the green and brown +tangles, while the far-sailing velella and the stay-at-home sea-squirts, +together with a variety of other sea-animals, find a nursery and shelter +in their youth in this quiet harbour of rest. + +And besides these casual visitors there are numberless creatures which +have lived and multiplied there, ever since I first visited the pool. +Tender red, olive-coloured, and green seaweeds, stony corallines, and +acorn-barnacles lining the floor, sea-anemones clinging to the sides, +sponges tiny and many-coloured hiding under the ledges, and limpets and +mussels wedged in the cracks. These can be easily seen with the naked +eye, but they are not the most numerous inhabitants; for these we must +search with a magnifying-glass, which will reveal to us wonderful +fairy-forms, delicate crystal vases with tiny creatures in them whose +transparent lashes make whirlpools in the water, living crystal bells so +tiny that whole branches of them look only like a fringe of hair, jelly +globes rising and falling in the water, patches of living jelly +clinging to the rocky sides of the pool, and a hundred other forms, some +so minute that you must examine the fine sand in which they lie under a +powerful microscope before you can even guess that they are there. + +[Illustration: Fig. 63. + +Group of seaweeds (natural size). + +1, _Ulva Linza._ 2, _Sphacelaria filicina._ 3, _Polysiphonia urceolata._ +4, _Corallina officinalis._] + +So it has proved a rich hunting-ground, where summer and winter, spring +and autumn, I find some form to put under my magic glass. There I can +watch it for weeks growing and multiplying under my care; moved only +from the aquarium, where I keep it supplied with healthy sea-water, to +the tiny transparent trough in which I place it for a few hours to see +the changes it has undergone. I could tell you endless tales of +transformations in these tiny lives, but I want to-day to show you a +few of my friends, most of which I brought yesterday fresh from the +pool, and have prepared for you to examine. + +[Illustration: Fig. 64. + +_Ulva lactuca_, a green seaweed, greatly magnified to show structure. +(After Oersted.) + +_s_, Spores in the cells. _ss_, Spores swimming out. _h_, Holes through +which spores have escaped.] + +Let us begin with seaweeds. I have said that there are three leading +colours in my pool--green, olive, and red--and these tints mark roughly +three kinds of weed, though they occur in an endless variety of shapes. +Here is a piece of the beautiful pale green seaweed, called the Laver or +Sea-lettuce, _Ulva Linza_ (1, Fig. 63), which grows in long ribbons in a +sunny nook in the water. I have placed under the first microscope a +piece of this weed which is just sending out young seaweeds in the shape +of tiny cells, with lashes very like those we saw coming from the +moss-flower, and I have pressed them in the position in which they would +naturally leave the plant (_ss_, Fig. 64.).[1] You will also see on this +slide several cells in which these tiny spores _s_ are forming, ready to +burst out and swim; for this green weed is merely a collection of cells, +like the single-celled plants on land. Each cell can work as a separate +plant; it feeds, grows, and can send out its own young spores. + + [1] The slice given in Fig. 64 is from a broader-leaved form, + _U. lactuca_, because this species, being composed of only one + layer of cells, is better seen. _Ulva linza_ is composed of two + layers of cells. + +This deep olive-green feathery weed (2, Fig. 63), of which a piece is +magnified under the next microscope (2, Fig. 65), is very different. It +is a higher plant, and works harder for its living, using the darker +rays of sunlight which penetrate into shady parts of the pool. So it +comes to pass that its cells divide the work. Those of the feathery +threads make the food, while others, growing on short stalks on the +shafts of the feather make and send out the young spores. + +[Illustration: Fig. 65. + +Three seaweeds of Fig. 63 much magnified to show fruits. (Harvey.) + +2, _Sphacelaria filicina._ 3, _Polysiphonia urceolata._ 4, _Corallina +officinalis._] + +Lastly, the lovely red threadlike weeds, such as this _Polysiphonia +urceolata_ (3, Fig. 63), carry actual urns on their stems like those of +mosses. In fact, the history of these urns (see No. 3, Fig. 65) is much +the same in the two classes of plants, only that instead of the urn +being pushed up on a thin stalk as in the moss, it remains on the +seaweed close down to the stem, when it grows out of the plant-egg, and +the tiny plant is shut in till the spores are ready to swim out. + +The stony corallines (4, Figs. 63 and 65), which build so much carbonate +of lime into their stems, are near relations of the red seaweeds. There +are plenty of them in my pool. Some of them, of a deep purple colour, +grow upright in stiff groups about three or four inches high; and +others, which form crusts over the stones and weeds, are a pale rose +colour; but both kinds, when the plant dies, leaving the stony skeleton +(1, Fig. 66), are a pure white, and used to be mistaken for corals. They +belong to the same order of plants as the red weeds, which all live in +shady nooks in the pools, and are the highest of their race. + +My pool is full of different forms of these four weeds. The green +ribbons float on the surface rooted to the sides of the pool and, as the +sun shines upon it, the glittering bubbles rising from them show that +they are working up food out of the air in the water, and giving off +oxygen. The brown weeds lie chiefly under the shelves of rocks, for they +can manage with less sunlight, and use the darker rays which pass by the +green weeds; and last of all, the red weeds and corallines, small and +delicate in form, line the bottom of the pool in its darkest nooks. + +And now if I hand round two specimens--one a coralline, and the other +something you do not yet know--I am sure you will say at first sight +that they belong to the same family, and, in fact, if you buy at the +seaside a group of seaweeds gummed on paper, you will most likely get +both these among them. Yet the truth is, that while the coralline (1, +Fig. 66) is a plant, the other specimen (2) which is called _Sertularia +filicula_, is an animal. + +[Illustration: Fig. 66. + +Coralline and Sertularia, to show likeness between the animal Sertularia +and the plant Coralline. + +1, _Corallina officinalis._ 2, _Sertularia filicula._] + +This special sertularian grows upright in my pool on stones or often on +seaweeds, but I have here (Fig. 67) another and much smaller one which +lives literally in millions hanging its cups downwards. I find it not +only under the narrow ledges of the pool sheltered by the seaweed, but +forming a fringe along all the rocks on each side of the cove near to +low-water mark, and for a long time I passed it by thinking it was of no +interest. But I have long since given up thinking this of anything, +especially in my pool, for my magic glass has taught me that there is +not even a living speck which does not open out into something +marvellous and beautiful. So I chipped off a small piece of rock and +brought the fringe home, and found, when I hung it up in clear sea water +as I have done over this glass trough (Fig. 67) and looked at it through +the lens, that each thread of the dense fringe, in itself not a quarter +of an inch deep, turns out to be a tiny sertularian with at least twenty +mouths. You can see this with your pocket lens even as it hangs here, +and when you have examined it you can by and by take off one thread and +put it carefully in the trough. I promise you a sight of the most +beautiful little beings which exist in nature. + +[Illustration: Fig. 67. + +_Sertularia tenella_, hanging from a splint of rock over a water trough. +Also piece enlarged to show the animal protruding.] + +Come and look at it after the lecture. It is a horny branched stem with +a double row of tiny cups all along each side (see Fig. 67). Out of +these cups there appear from time to time sixteen minute transparent +tentacles as fine as spun glass, which wave about in the water. If you +shake the glass a little, in an instant each crystal star vanishes into +its cup, to come out again a few minutes later; so that now here, now +there, the delicate animal-flowers spread out on each side of the stem, +and the tree is covered with moving beings. These tentacles are feelers, +which lash food into a mouth and stomach in each cup, where it is +digested and passed, through a hole in the bottom, along a jelly thread +which runs down the stem and joins all the mouths together. In this way +the food is distributed all over the tree, which is, in fact, one animal +with many feeding-cups. Some day I will show you one of these cups with +the tentacles stretched out and mounted on a slide, so that you can +examine a tentacle with a very strong magnifying power. You will then +see that it is dotted over with cells, in which are coiled fine +threads. The animal uses these threads to paralyse the creatures on +which it feeds, for at the base of each thread there is a poison gland. + +In the larger Sertularia (2, Fig. 66) the whole branched tree is +connected by jelly threads running through the stem, and all the +thousands of mouths are spread out in the water. One large form called +the sea-fir _Sertularia cupressina_ grows sometimes three feet high, and +bears as many as a hundred thousand cups, with living mouths, on its +branches. + +The next of my minute friends I can only show to the class in a diagram, +but you will see it under the fourth microscope by and by. I had great +trouble in finding it yesterday, though I knew its haunts upon the green +weed, for it is so minute and transparent that even when the weed is in +a trough a magnifying-glass will scarcely detect it. And I must warn you +that if you want to know any of the minute creatures we are studying, +you must visit one place constantly. You may in a casual way find many +of them on seaweed, or in the damp ooze and mud, but it will be by +chance only; to look for them with any certainty you must take trouble +in making their acquaintance. + +Turning then to the diagram (Fig. 68) I will describe it as I hope you +will see it under the microscope--a curious tiny, perfectly transparent +open-mouthed vase standing upright on the weed, and having an equally +transparent being rising up in it and waving its tiny lashes in the +water. This is really all one animal, the vase _hc_ being the horny +covering or carapace of the body, which last stands up like a tube in +the centre. If you watch carefully, you may even see the minute atoms of +food twisting round inside the tube until they are digested, after they +have been swept in at the wide open mouth by the whirling lashes. You +will see this more clearly if you put a little rice-flour, very minutely +powdered and coloured by carmine, into the water; for you can trace +these red atoms into some round spaces called _vacuoles_ which are +dotted over the body of the animal, and are really globules of watery +fluid in which the food is probably partly digested. + +[Illustration: Fig. 68. + +_Thuricolla folliculata_ and _Chilomonas amygdalum_. (Saville Kent.) + +1, Thuricolla erect; 2, retracted; 3, dividing. 4, _Chilomonas +amygdalum_. _hc_, Horny carapace. _cv_, Contractile vesicle. _v_, +Closing valves.] + +You will notice, however, one round clear space (_cv_) into which they +do not go, and after a time you will be able to observe that this round +spot closes up or contracts very quickly, and then expands again very +slowly. As it expands it fills with a clear fluid, and naturalists have +not yet decided exactly what work it does. It may serve the animal +either for breathing, or as a very simple heart, making the fluids +circulate in the tube. The next interesting point about this little +being is the way it retreats into its sheltering vase. Even while you +are watching, it is quite likely it may all at once draw itself down to +the bottom as in No. 2, and folding down the valves _v_, _v_ of horny +teeth which grow on each side, shut itself in from some fancied danger. +Another very curious point is that, besides sending forth young ones, +these creatures multiply by dividing in two (see No. 3, Fig. 68), each +one closing its own part of the vase into a new home. + +There are hundreds of these _Infusoria_, as they are called, in my pond, +some with vases, some without, some fixed to weeds and stones, others +swimming about freely. Even in the water-trough in which this Thuricolla +stands, I saw several smaller forms, and the next microscope has a +trough filled with the minutest form of all, called a Monad (No. 4, Fig. +68). These are so small that 2000 of them would lie side by side in an +inch; that is, if you could make them lie at all, for they are the most +restless little beings, darting hither and thither, scarcely even +halting except to turn back. And yet though there are so many of them, +and as far as we know they have no organs of sight, they never run up +against each other, but glide past more cleverly than any clear-sighted +fish. These creatures are mostly to be found among decaying seaweed, and +though they are so tiny, you can still see distinctly the clear space +(_cv_) contracting and expanding within them. + +But if there are so many thousands of mouths to feed, on the tree-like +_Sertulariae_ as well as in all these _Infusoria_, where does the food +come from? + +Partly from the numerous atoms of decaying life all around, and the +minute eggs of animals and spores of plants; but besides these, the pool +is full of minute living plants--small jelly masses with solid coats of +flint which are moulded into most lovely shapes. Plants formed of jelly +and flint! You will think I am joking, but I am not. These plants, +called _Diatoms_, which live both in salt and fresh water, are single +cells feeding and growing just like those we took from the water-butt +(Fig. 29, p. 78), only that instead of a soft covering they build up a +flinty skeleton. They are so small, that many of them must be magnified +to fifty times their real size before you can even see them distinctly. +Yet the skeletons of these almost invisible plants are carved and +chiselled in the most delicate patterns. I showed you a group of these +in our lecture on magic glasses (p. 39), and now I have brought a few +living ones that we may learn to know them. The diagram (Fig. 69) shows +the chief forms you will see on the different slides. + +[Illustration: Fig. 69. + +Living diatoms. + +_a_, _Cocconema lanceolatum_. _b_, _Bacillaria paradoxa_. +_c_, _Gomphonema marinum_. _d_, _Diatoma hyalina_.] + +The first one, _Bacillaria paradoxa_ (_b_, Fig. 69), looks like a number +of rods clinging one to another in a string, but each one of these is a +single-celled plant with a jelly cell surrounding the flinty skeleton. +You will see that they move to and fro over each other in the water. + +[Illustration: Fig. 70. + +A diatom (_Diatoma vulgare_) growing. + +_a_, _b_, Flint skeleton inside the jelly-cell. _a_, _c_ and _d_, _b_, +Two flint skeletons formed by new valves, _c_ and _d_, forming within +the first skeleton.] + +The next two forms, _a_ and _c_, look much more like plants, for the +cells arrange themselves on a jelly stem, which by and by disappears, +leaving only the separate flint skeletons such as you see in Fig. 16. +The last form, _d_, is something midway between the other forms, the +separate cells hang on to each other and also on to a straight jelly +stem. + +Another species of Diatoma (Fig. 70) called _Diatoma vulgare_, is a very +simple and common form, and will help to explain how these plants grow. +The two flinty valves _a_, _b_ inside the cell are not quite the same +size; the older one _a_ is larger than the younger one _b_ and fits over +it like the cover of a pill-box. As the plant grows, the cell enlarges +and forms two more valves, one _c_ fitting into the cover _a_, so as to +make a complete box _ac_, and a second, _d_, back to back with _c_, +fitting into the valve _b_, and making another complete box _bd_. This +goes on very rapidly, and in this plant each new cell separates as it is +formed, and the free diatoms move about quite actively in the water. + +If you consider for a moment, you will see that, as the new valves +always fit into the old ones, each must be smaller than the last, and so +there comes a time when the valves have become too small to go on +increasing. Then the plant must begin afresh. So the two halves of the +last cell open, and throwing out their flinty skeletons, cover +themselves with a thin jelly layer, and form a new cell which grows +larger than any of the old ones. These, which are spore-cells, then form +flinty valves inside, and the whole thing begins again. + +Now though the plants themselves die, or become the food of minute +animals, the flinty skeletons are not destroyed, but go on accumulating +in the waters of ponds, lakes, rivers, and seas, all over the world. +Untold millions have no doubt crumbled to dust and gone back into the +waters, but untold millions also have survived. The towns of Berlin in +Europe and of Richmond in the United States are actually built upon +ground called "infusorial earth," composed almost entirely of valves of +these minute diatoms which have accumulated to a thickness of more than +eighty feet! Those under Berlin are fresh-water forms, and must have +lived in a lake, while those of Richmond belong to salt-water forms. +Every inch of the ground under those cities represents thousands and +thousands of living plants which flourished in ages long gone by, and +were no larger than those you will see presently under the microscope. + +These are a very few of the microscopic inhabitants of my pond, but, as +you will confuse them if I show you too many, we will conclude with two +rather larger specimens, and examine them carefully. The first, called +the Cydippe, is a lovely, transparent living ball, which I want to +explain to you because it is so wondrously beautiful. The second, the +Sea-mat or Flustra, looks like a crumpled drab-coloured seaweed, but is +really composed of many thousands of grottos, the homes of tiny +sea-animals. + +[Illustration: Fig. 71. + +_Cydippe Pileus._ + +1, Animal with tentacles _t_, bearing small tendrils _t'_. 2, Body of +animal enlarged. _m_, Mouth. _c_, Digestive cavity. _s_, Sac into which +the tentacles are withdrawn. _p_, Bands with comb-like plates. 3, +Portion of a band enlarged to show the moving plates _p_.] + +Let us take the Cydippe first (1, Fig. 71). I have six here, each in a +separate tumbler, and could have brought many more, for when I dipped my +net in the pool yesterday such numbers were caught in it that I believe +the retreating tide must just have left a shoal behind. Put a tumbler on +the desk in front of you, and if the light falls well upon it you will +see a transparent ball about the size of a large pea marked with eight +bright bands, which begin at the lower end of the ball and reach nearly +to the top, dividing the outside into sections like the ribs of a melon. +The creature is so perfectly transparent that you can count all the +eight bands. + +At the top of the ball is a slight bulge which is the mouth (_m_ 2, Fig. +71), and from it, inside the ball, hangs a long bag or stomach, which +opens below into a cavity c, from which two canals branch out, one on +each side, and these divide again into four canals which go one into +each of the tubes running down the bands. From this cavity the food, +which is digested in the stomach, is carried by the canals all over the +body. The smaller tubes which branch out of these canals cannot be seen +clearly without a very strong lens, and the only other parts you can +discern in this transparent ball are two long sacs on each side of the +lower end. These are the tentacle sacs, in which are coiled up the +tentacles, which we shall describe presently. Lastly, you can notice +that the bands outside the globe are broader in the middle than at the +ends, and are striped across by a number of ridges. + +In moving the tumblers the water has naturally been shaken, and the +creature being alarmed will probably at first remain motionless. But +very soon it will begin to play in the water, rising and falling, and +swimming gracefully from side to side. Now you will notice a curious +effect, for the bands will glitter and become tinged with prismatic +colours, till, as it moves more and more rapidly these colours, +reflected in the jelly, seem to tinge the whole ball with colours like +those on a soap-bubble, while from the two sacs below come forth two +long transparent threads like spun glass. At first these appear to be +simple threads, but as they gradually open out to about four or five +inches, smaller threads uncoil on each side of the line till there are +about fifty on each line. These short _tendrils_ are never still for +long; as the main threads wave to and fro, some of the shorter ones coil +up and hang like tiny beads, then these uncoil and others roll up, so +that these graceful floating lines are never two seconds alike. + +We do not really know their use. Sometimes the creature anchors itself +by them, rising and falling as they stretch out or coil up; but more +often they float idly behind it in the water. At first you would perhaps +think that they served to drive the ball through the water, but this is +done by a special apparatus. The cross ridges which we noticed on the +bands are really flat comb-like plates (_p_, Fig. 71), of which there +are about twenty or thirty on each band; and these vibrate very rapidly, +so that two hundred or more paddles drive the tiny ball through the +water. This is the cause of the prismatic colours; for iridescent tints +are produced by the play of light upon the glittering plates, as they +incessantly change their angle. Sometimes they move all at once, +sometimes only a few at a time, and it is evident the creature controls +them at will. + +This lovely fairy-like globe, with its long floating tentacles and +rainbow tints, was for a long time classed with the jelly-fish; but it +really is most nearly related to sea-anemones, as it has a true central +cavity which acts as a stomach, and many other points in common with the +_Actinozoa_. We cannot help wondering, as the little being glides hither +and thither, whether it can see where it is going. It has nerves of a +low kind which start from a little dark spot (_ng_), exactly at the +south pole of the ball, and at that point a sense-organ of some kind +exists, but what impression the creature gains from it of the world +outside we cannot tell. + +I am afraid you may think it dull to turn from such a beautiful being as +this, to the grey leaf which looks only like a dead dry seaweed; yet you +will be wrong, for a more wonderful history attaches to this crumpled +dead-looking leaf than to the lovely jelly-globe. + +First of all I will pass round pieces of the dry leaf (_r_, Fig. 72), +and while you are getting them I will tell you where I found the living +ones. Great masses of the Flustra, as it is called, line the bottom and +sides of my pool. They grow in tufts, standing upright on the rock, and +looking exactly like hard grey seaweeds, while there is nothing to lead +you to suspect that they are anything else. Yesterday I chipped off very +carefully a piece of rock with a tuft upon it, and have kept it since in +a glass globe by itself with sea-water, for the little creatures living +in this marine city require a very good supply of healthy water and air. +I have called it a "marine city," and now I will tell you why. Take the +piece in your hand and run your finger gently up and down it; you will +glide quite comfortably from the lower to the higher part of the leaf, +but when you come back you will feel your finger catch slightly on a +rough surface. Your pocket lens will show why this is, for if you look +through it at the surface of the leaf you will see it is not smooth, but +composed of hundreds of tiny alcoves with arched tops; and on each side +of these tops stand two short blunt spines (see 2, Fig. 72), making four +in all, pointing upwards, so as partly to cover the alcove above. As +your finger went up it glided over the spines, but on coming back it met +their points. This is all you can see in the dead specimen; I must show +you the rest by diagrams, and by and by under the microscope. + +[Illustration: Fig. 72. + +The Sea-mat or Flustra (_Flustra foliacea._) + +1, Natural size. 2, Much magnified. _s_, Slit caused by drawing in of +the animal _a_.] + +First, then, in the living specimen which I have here, those alcoves are +not open as in the dead piece, but covered over with a transparent skin, +in which, near the top of the alcove just where the curve begins, is a +slit (_s_ 2, Fig. 72). Unfortunately the membrane covering this alcove +is too dense for you to distinguish the parts within. Presently, +however, if you are watching a piece of this living leaf in a flat +water-cell under the microscope, you will see the slit slowly open, and +begin to turn as it were inside out, exactly like the finger of a +glove, which has been pushed in at the tip, gradually rises up when you +put your finger inside it. As this goes on, a bundle of threads appears, +at first closed like a bud, but gradually opening out into a crown of +tentacles (_a_, Fig. 72), each one clothed with hairs. Then you will see +that the slit was not exactly a slit after all, but the round edge where +the sac was pushed in. Ah! you will say, you are now showing me a polyp +like those on the sertularian tree. Not so fast, my friend; you have not +yet studied what is still under the covering skin and hidden in the +living animal. I have, however, prepared a slide with this membrane +removed (see Fig. 73), and there you can observe the different parts, +and learn that each one of these alcoves contains a complete animal, and +not merely one among many mouths, like the polyp on the Sertularia. + +[Illustration: Fig. 73. + +Diagram of the animal in the Flustra or Sea-mat. + +1, Animal protruding. 2, Animal retracted in the sheath. _sh_, Covering +sheath. _s_, Slit. _t_, Tentacles. _m_, Mouth. _th_, Throat. _st_, +Stomach. _i_, Intestine. _r_, Retractor muscle. _e_, Egg-forming parts. +_g_, Nerve-ganglion.] + +Each of these little beings (_a_, Fig 72) living in its alcove has a +mouth, throat, stomach, intestine, muscles, and nerves starting from the +ganglion of nervous matter, besides all that is necessary for producing +eggs and sending forth young ones. You can trace all these under the +microscope (see 2, Fig. 73) as the creature lies curiously doubled up in +its bed, with its body bent in a loop; the intestine _i_, out of which +the refuse food passes, coming back close up to the slit. When it is at +rest, the top of the sac in which it lies is pulled in by the retractor +muscle _r_, and looks, as I have said, like the finger of a glove with +the top pushed in. When it wishes to feed, this top is drawn out by +muscles running round the sac, and the tentacles open and wave in the +water (1, Fig. 73). + +Look now at the alcoves, the homes of these animals; see how tiny they +are and how closely they fit together. Mr. Gosse, the naturalist, has +reckoned that there are 6720 alcoves in a square inch; then if you turn +the leaf over you will see that there is another set, fixed back to back +with these, on the other side, making in all 13,440 alcoves. Now a +moderate-sized leaf of flustra measures about three square inches, +taking all the rounded lobes into account, so you will see we get 40,320 +as a rough estimate of the number of beings on this one leaf. But if you +look at this tuft I have brought, you will find it is composed of twelve +such leaves, and this after all is a very small part of the mass growing +round my pool. Was I wrong, then, when I said that my miniature ocean +contains as many millions of beings as there are stars in the heavens? + +You will want to know how these leaves grew, and it is in this way. +First a little free swimming animal, a mere living sac provided with +lashes, settles down and grows into one little horny alcove, with its +live creature inside, which in time sends off from it three to five +buds, forming alcoves all round the top and sides of the first one, +growing on to it. These again bud out, and you can thus easily +understand that, in this way, in time a good-sized leaf is formed. +Meanwhile the creatures also send forth new swimming cells, which settle +down near to begin new leaves, and thus a tuft is formed; and long after +the beings in earlier parts of the leaf have died and left their alcoves +empty, those round the margin are still alive and spreading. + +With this history we must stop for to-day, and I expect it will be many +weeks before you have thoroughly examined the specimens of each kind +which I have put in the aquarium. If you can trace the spore-cells and +urns in the seaweeds, observe the polyps in the Sertularia, and count +the number of mouths on a branch of my animal fringe (_Sertularia +tenella_); if you make acquaintance with the Thuricolla in its vase, and +are fortunate enough to see one divide in two; if you learn to know some +of the beautiful forms of diatoms, and can picture to yourselves the +life of the tiny inhabitants of the Flustra; then you will have used +your microscope with some effect, and be prepared for an expedition to +my pool, where we will go together some day to seek new treasures. + + + + +CHAPTER IX + +THE DARTMOOR PONIES, + +OR + +THE WANDERINGS OF THE HORSE TRIBE + + +[Illustration] + +Put away the telescopes and microscopes to-day, boys, the holidays are +close at hand, and we will take a rest from peeping and peering till we +come back in the autumn laden with specimens for the microscope, while +the rapidly darkening evenings will tempt us again on to the lawn +star-gazing. On this our last lecture-day I want you to take a journey +with me which I took in imagination a few days ago, as I lay on my back +on the sunny moor and watched the Dartmoor ponies. + +It was a calm misty morning one day last week, giving promise of a +bright and sunny day, when I started off for a long walk across the moor +to visit the famous stone-circles, many of which are to be found not +far off the track, called Abbot's Way, leading from Buckfast Abbey, on +the Dart, to the Abbey of Tavistock, on the Tavy. + +My mind was full of the olden times as I pictured to myself how, seven +hundred years or more ago, some Benedictine monk from Tavistock Abbey, +in his black robe and cowl, paced this narrow path on his way to his +Cistercian brethren at Buckfast, meeting some of them on his road as +they wandered over the desolate moor in their white robes and black +scapularies in search of stray sheep. For the Cistercians were shepherds +and wool-weavers, while the Benedictines devoted themselves to learning, +and the track of about twenty-five miles from one abbey to the other, +which still remains, was worn by the members of the two communities and +their dependents, the only variety in whose lives consisted probably in +these occasional visits one to the other. + +Yet even these monks belonged to modern times compared to the ancient +Britons who raised the stone-circles, and buried their dead in the +barrows scattered here and there over the moor; and my mind drifted back +to the days when, long before that pathway was worn, men clad in the +skins of beasts hunted wild animals over the ground on which I was +treading, and lived in caves and holes of the ground. + +I wondered, as I thought of them, whether the cultured monks and the +uncivilised Britons delighted as much in the rugged scenery of the moor +as I did that morning. For many miles in front of me the moor stretched +out wild and treeless; the sun was shining brightly upon the mass of +yellow furze and deep-red heather, drawing up the moisture from the +ground, and causing a kind of watery haze to shimmer over the landscape; +while the early mist was rising off the _tors_, or hill-tops, in the +distance, curling in fanciful wreaths around the rugged and stony +summits, as it dispersed gradually in the increasing heat of the day. + +The cattle which were scattered in groups here and there feeding on the +dewy grass were enjoying the happiest time of the year. The moor, which +in winter affords them scarcely a bare subsistence, is now richly +covered with fresh young grass, and the sturdy oxen fed solemnly and +deliberately, while the wild Dartmoor ponies and their colts scampered +joyously along, shaking their manes and long flowing tails, and neighing +to each other as they went; or clustered together on some verdant spot, +where the colts teased and bit each other for fun, as they gambolled +round their mothers. + +It was a pleasure, there on the open moor, with the lark soaring +overhead, and the butterflies and bees hovering among the sweet-smelling +furze blossoms, to see horses free and joyous, with no thought of bit or +bridle, harness or saddle, whose hoofs had never been handled by the +shoeing-smith, nor their coats touched with the singeing iron. Those +little colts, with their thick heads, shaggy coats, and flowing tails, +will have at least two years more freedom before they know what it is to +be driven or beaten. Only once a year are they gathered together, +claimed by their owners and branded with an initial, and then left +again to wander where they will. True, it is a freedom which sometimes +has its drawbacks, for if the winter is severe the only food they can +get will be the furze-tops, off which they scrape the snow with their +feet; yet it is very precious in itself, for they can gallop when and +where they choose, with head erect, sniffing at the wind and crying to +each other for the very joy of life. + +Now as I strolled across the moor and watched their gambols, thinking +how like free wild animals they seemed, my thoughts roamed far away, and +I saw in imagination scenes where other untamed animals of the horse +tribe are living unfettered all their lives long. + +First there rose before my mind the level grass-covered pampas of South +America, where wild horses share the boundless plains with troops of the +rhea, or American ostrich, and wander, each horse with as many mares as +he can collect, in companies of hundreds or even thousands in a troop. +These horses are now truly wild, and live freely from youth to age, +unless they are unfortunate enough to be caught in the more inhabited +regions by the lasso of the hunter. In the broad pampas, the home of +herds of wild cattle, they dread nothing. There, as they roam with one +bold stallion as their leader, even beasts of prey hesitate to approach +them, for, when they form into a dense mass with the mothers and young +in their centre, their heels deal blows which even the fierce jaguar +does not care to encounter, and they trample their enemy to death in a +very short time. Yet these are not the original wild horses we are +seeking, they are the descendants of tame animals, brought from Europe +by the Spaniards to Buenos Ayres in 1535, whose descendants have +regained their freedom on the boundless pampas and prairies. + +As I was picturing them careering over the plains, another scene +presented itself and took their place. Now I no longer saw around me +tall pampas-grass with the long necks of the rheas appearing above it, +for I was on the edge of a dreary scantily covered plain between the +Aral Sea and the Balkash Lake in Tartary. To the south lies a barren +sandy desert, to the north the fertile plains of the Kirghiz steppes, +where the Tartar feeds his flocks, and herds of antelopes gallop over +the fresh green pasture; and between these is a kind of no-man's land, +where low scanty shrubs and stunted grass seemed to promise but a poor +feeding-ground. + +Yet here the small long-legged but powerful "Tarpans," the wild horses +of the treeless plains of Russia and Tartary, were picking their morning +meal. Sturdy wicked little fellows they are, with their shaggy +light-brown coats, short wiry manes, erect ears, and fiery watchful +eyes. They might well be supposed to be true wild horses, whose +ancestors had never been tamed by man; and yet it is more probable that +even they escaped in early times from the Tartars, and have held their +own ever since, over the grassy steppes of Russia and on the confines of +the plains of Tartary. Sometimes they live almost alone, especially on +the barren wastes where they have been seen in winter, scraping the snow +off the herbage as our ponies do on Dartmoor. At other times, as in the +south of Russia, where they wander between the Dnieper and the Don, they +gather in vast herds and live a free life, not fearing even the wolves, +which they beat to the ground with their hoofs. From one green oasis to +another they travel over miles of ground. + + "A thousand horse--and none to ride! + With flowing tail, and flying mane, + Wide nostrils--never stretch'd by pain, + Mouths bloodless to the bit or rein, + And feet that iron never shod, + And flanks unscarr'd by spur or rod. + A thousand horse, the wild, the free, + Like waves that follow o'er the sea."[1] + + [1] Byron's _Mazeppa_. + +As I followed them in their course I fancied I saw troops of yet another +animal of the horse tribe, the "Kulan," or _Equus hemionus_, which is a +kind of half horse, half ass (Fig. 74), living on the Kirghiz steppes of +Tartary and spreading far beyond the range of the Tarpan into Tibet. +Here at last we have a truly wild animal, never probably brought into +subjection by man. The number of names he possesses shows how widely he +has spread. The Tartars call him "Kulan," the Tibetans "Kiang," while +the Mongolians give him the unpronounceable name of "Dschiggetai." He +will not submit to any of them, but if caught and confined soon breaks +away again to his old life, a "free and fetterless creature." + +[Illustration: Fig. 74. + +_Equus hemionus_, "Kiang" or "Kulan," the Horse-ass of Tartary and +Tibet. (Brehm.)] + +No one has ever yet settled the question whether he is a horse or an +ass, probably because he represents an animal truly between the two. +His head is graceful, his body light, his legs slender and fleet, yet +his ears are long and ass-like; he has narrow hoofs, and a tail with a +tuft at the end like all the ass tribe; his colour is a yellow brown, +and he has a short dark mane and a long dark stripe down his back as a +donkey has, though this last character you may also see in many of our +Devonshire ponies. Living often on the high plateaux, sometimes as much +as 1500 feet above the sea, this "child of the steppes" travels in large +companies even as far as the rich meadows of Central Asia; in summer +wandering in green pastures, and in winter seeking the hunger-steppes +where sturdy plants grow. And when autumn comes the young steeds go off +alone to the mountain heights to survey the country around and call +wildly for mates, whom, when found, they will keep close to them through +all the next year, even though they mingle with thousands of others. + +[Illustration: Fig. 75. + +Przevalsky's Wild Horse, the "Kertag" or "Statur."] + +Till about ten years ago the _Equus hemionus_ was the only truly wild +horse known, but in the winter of 1879-80 the Russian traveller +Przevalsky brought back from Central Asia a much more horse-like animal, +called by the Tartars "Kertag" and by the Mongols "Statur." It is a +clumsy, thick-set, whitish-gray creature with strong legs and a large, +heavy, reddish-coloured head; its legs have a red tint down to the +knees, beyond which they are blackish down to the hoofs. But the ears +are small, and it has the broad hoofs of the true horse, and warts on +his hind legs, which no animal of the ass tribe has. This horse, like +the Kiang, travels in small troops of from five to fifteen, led through +the wildest parts of the Dsungarian desert, between the Altai and +Tianschan Mountains, by an old stallion. They are extremely shy, and +see, hear, and smell very quickly, so that they are off like lightning +whenever anything approaches them. + +So having travelled over America, Europe, and Asia, was my quest ended? +No; for from the dreary Asiatic deserts my thoughts wandered to a far +warmer and more fertile land, where between the Blue Nile and the Red +Sea rise the lofty highlands of Abyssinia, among which the African wild +ass (_Asinus taeniopus_), the probable ancestor of our donkeys, feeds in +troops on the rich grasses of the slopes, and then onwards to the bank +of a river in Central Africa where on the edge of a forest, with rich +pastures beyond, elephants and rhinoceroses, antelopes and buffaloes, +lions and hyaenas, creep down in the cool of the evening to slake their +thirst in the flowing stream. There I saw the herds of Zebras in all +their striped beauty coming down from the mountain regions to the north, +and mingling with the darker-coloured but graceful quaggas from the +southern plains, and I half-grieved at the thought how these untamed and +free rovers are being slowly but surely surrounded by man closing in +upon them on every side. + +I might now have travelled still farther in search of the Onager, or +wild ass of the Asiatic and Indian deserts, but at this point a more +interesting and far wider question presented itself, as I flung myself +down on the moor to ponder over the early history of all these tribes. + +Where have they all come from? Where shall we look for the first +ancestors of these wild and graceful animals? For the answer to this +question I had to travel back to America, to those Western United States +where Professor Marsh has made such grand discoveries in horse history. +For there, in the very country where horses were supposed never to have +been before the Spaniards brought them a few centuries ago, we have now +found the true birthplace of the equine race. + +Come back with me to a time so remote that we cannot measure it even by +hundreds of thousands of years, and let us visit the territories of Utah +and Wyoming. Those highlands were very different then from what they are +now. Just risen out of the seas of the Cretaceous Period, they were then +clothed with dense forests of palms, tree-ferns, and screw-pines, +magnolias and laurels, interspersed with wide-spreading lakes, on the +margins of which strange and curious animals fed and flourished. There +were large beasts with teeth like the tapir and the bear, and feet like +the elephant; and others far more dangerous, half bear, half hyaena, +prowling around to attack the clumsy paleotherium or the anoplotherium, +something between a rhinoceros and a horse, which grazed by the +waterside, while graceful antelopes fed on the rich grass. And among +these were some little animals no bigger than foxes, with four toes and +a splint for the fifth, on their front feet, and three toes on the hind +ones. + +These clumsy little animals, whose bones have been found in the rocks of +Utah and Wyoming, have been called _Eohippus_, or horses of the dawn, +by naturalists. They were animals with real toes, yet their bones and +teeth show that they belonged to the horse tribe, and already the fifth +toe common to most other toed animals was beginning to disappear. + +This was in the Eocene period, and before it passed away with its +screw-pines and tree-ferns, another rather larger animal, called the +_Orohippus_, had taken the place of the small one, and he had only four +toes on his front feet. The splint had disappeared, and as time went on +still other animals followed, always with fewer toes, while they gained +slender fleet legs, together with an increase in size and in +gracefulness. First one as large as a sheep (_Mesohippus_) had only +three toes and a splint. Then the splint again disappeared, and one +large and two dwindling toes only remained, till finally these two +became mere splints, leaving one large toe or hoof with almost +imperceptible splints, which may be seen on the fetlock of a horse's +skeleton. + +The diagram (Fig 76) shows these splints in the horse's or ass's foot of +to-day. For you must notice that a horse's foot really begins at the +point _w_ which we call his knee in the front legs, and at his hock _h_ +in the hind legs. His true knee _k_ and elbow _e_ are close up to the +body. What we call his foot or hoof is really the end of the strong, +broad, middle toe _t_ covered with a hoof, and farther up his foot at +_s_ and _s_ we can feel two small splints, which are remains of two +other toes. + +Meanwhile during these long succeeding ages while the foot was +lengthening out into a slender limb the animals became larger, more +powerful, and more swift, the neck and head became longer and more +graceful, the brain-case larger in front and the teeth decreased in +number, so that there is now a large gap between the biting teeth _i_ +and the grinding teeth _g_ of a horse. Their slender limbs too became +more flexible and fit for running and galloping, till we find the whole +skeleton the same in shape, though not in size, as in our own horses and +asses now. + +[Illustration: Fig. 76. + +Skeleton of Horse or Ass. + +_i_, Incisor teeth. _g_, Grinding teeth, with the gap between the two as +in all grass-feeders. _k_, Knee. _h_, Hock or heel. _f_, Foot. _s_, +Splints or remains of the two lost toes. _e_, Elbow. _w_, Wrist. _ha_, +Hand-bone. _t_, middle toe of three joints, 1, 2, 3 forming the hoof.] + +They did not, however, during all this time remain confined to America, +for, from the time when they arrived at an animal called _Miohippus_, or +lesser horse, which came after the Mesohippus and had only three toes +on each foot, we find their remains in Europe, where they lived in +company with the giraffes, opossums, and monkeys which roamed over these +parts in those ancient times. Then a little later we find them in Africa +and India; so that the horse tribe, represented by creatures about as +large as donkeys, had spread far and wide over the world. + +And now, curiously enough, they began to forsake, or to die out in, the +land of their birth. Why they did so we do not know; but while in the +old world as asses, quaggas, and zebras, and probably horses, they +flourished in Asia, Europe, and Africa, they certainly died out in +America, so that ages afterwards, when that land was discovered, no +animal of the horse tribe was found in it. + +And the true horse, where did he arise? Born and bred probably in +Central Asia from some animal like the "Kulan," or the "Kertag," he +proved too useful to savage tribes to be allowed his freedom, and it is +doubtful whether in any part of the world he escaped subjection. In our +own country he probably roamed as a wild animal till the savages, who +fed upon him, learned in time to put him to work; and when the Romans +came they found the Britons with fine and well-trained horses. + +Yet though tamed and made to know his master he has, as we have seen, +broken loose again in almost all parts of the world--in America on the +prairies and pampas, in Europe and Asia on the steppes, and in Australia +in the bush. And even in Great Britain, where so few patches of +uncultivated land still remain, the young colts of Dartmoor, Exmoor, +and Shetland, though born of domesticated mothers, seem to assert their +descent from wild and free ancestors as they throw out their heels and +toss up their heads with a shrill neigh, and fly against the wind with +streaming manes and outstretched tails as the Kulan, the Tarpan, and the +Zebra do in the wild desert or grassy plain. + + + + +CHAPTER X + +THE MAGICIAN'S DREAM OF ANCIENT DAYS. + + +[Illustration] + +The magician sat in his armchair in the one little room in the house +which was his, and his only, besides the observatory. And a strange room +it was. The walls were hung with skulls and bones of men and animals, +with swords, daggers, and shields, coats of mail, and bronze +spear-heads. The drawers, many of which stood open, contained +flint-stones chipped and worn, arrowheads of stone, jade hatchets +beautifully polished, bronze buckles and iron armlets; while scattered +among these were pieces of broken pottery, some rough and only +half-baked, others beautifully finished, as the Romans knew how to +finish them. Rough needles made of bone lay beside bronze knives with +richly-ornamented handles and, most precious of all, on the table by the +magician's side lay a reindeer antler, on which was roughly carved the +figure of the reindeer itself. + +He had been enjoying a six weeks' holiday, and he had employed it in +visiting some of the bone caves of Europe to learn about the men who +lived in them long, long ago. He had been to the south of France to see +the famous caves of the Dordogne, to Belgium to the caves of Engis and +Engihoul, to the Hartz Mountains and to Hungary. Then hastening home he +had visited the chief English caves in Yorkshire, Wales, and Devonshire. + +Now that he had returned to his college, his mind was so full of facts, +that he felt perplexed how to lay before his class the wonderful story +of the life of man before history began. And as the day was hot, and the +very breeze which played around him made him feel languid and sleepy, he +fell into a reverie--a waking dream. + + * * * * * + +First the room faded from his sight, then the trim villages disappeared; +the homesteads, the corn-fields, the grazing cattle, all were gone, and +he saw the whole of England covered with thick forests and rough +uncultivated land. From the mountains in the north, glaciers were to be +seen creeping down the valleys between dense masses of fir and oak, pine +and birch; while the wild horse, the bison, and the Irish elk were +feeding on the plains. As he looked southward and eastward he saw that +the sea no longer washed the shores, for the English and Irish Channels +were not yet scooped out. The British Isles were still part of the +continent of Europe, so that animals could migrate overland from the +far south, up to what is now England, Scotland, and Ireland. Many of +these animals, too, were very different from any now living in the +country, for in the large rivers of England he saw the hippopotamus +playing with her calf, while elephants and rhinoceroses were drinking at +the water's edge. Yet these strange creatures did not have all the +country to themselves--wolves, bears, and foxes prowled in the woods, +large beavers built their dams across the streams, and here and there +over the country human beings were living in caves and holes of the +earth. + +It was these men chiefly who attracted the magician's attention, and +being curious to know how they lived, he turned towards a cave, at the +mouth of which was a group of naked children who were knocking pieces of +flint together, trying to strike off splinters and make rough flint +tools, such as they saw their fathers use. Not far off from them a woman +with a wild beast's skin round her waist was gathering firewood, another +was grubbing up roots, and another, venturing a little way into the +forest, was searching for honey in the hollows of the tree trunks. + +All at once in the dusk of the evening a low growl and a frightened cry +were heard, and the women rushed towards the cave as they saw near the +edge of the forest a huge tiger with sabre-shaped teeth struggling with +a powerful stag. In vain the deer tried to stamp on his savage foe or to +wound him with his antlers; the strong teeth of the tiger had penetrated +his throat, and they fell struggling together as the stag uttered his +death-cry. Just at that moment loud shouts were heard in the forest, and +the frightened women knew that help was near. + +[Illustration: Fig. 77. + +Palaeolithic times.] + +One after another, several men, clothed in skins hung over one shoulder +and secured round the waist, rushed out of the thicket, their hair +streaming in the wind, and ran towards the tiger. They held in their +hands strange weapons made of rough pointed flints fastened into handles +by thongs of skin, and as the tiger turned upon them with a cry of rage +they met him with a rapid shower of blows. The fight raged fiercely, +for the beast was strong and the weapons of the men were rude, but the +tiger lay dead at last by the side of his victim. His skin and teeth +were the reward of the hunters, and the stag he had killed became their +prey. + +How skilfully they hacked it to pieces with their stone axes, and then +loading it upon their shoulders set off up the hill towards the cave, +where they were welcomed with shouts of joy by the women and children! + +[Illustration: Fig. 78. + +Palaeolithic relics. + +1, Bone needle, from a cave at La Madeleine, 1/2 size. 2, Tooth of +Machairodus or sabre-toothed tiger, from Kent's Cavern, 1/2 size. 3, +Rough stone implement, from Kent's Cavern, 1/4 size.] + +Then began the feast. First fires were kindled slowly and with +difficulty by rubbing a sharp-pointed stick in a groove of softer wood +till the wood-dust burst into flame; then a huge pile was lighted at the +mouth of the cave to cook the food and keep off wild beasts. How the +food was cooked the magician could not see, but he guessed that the +flesh was cut off the bones and thrust in the glowing embers, and he +watched the men afterwards splitting open the uncooked bones to suck out +the raw marrow which savages love. + +After the feast was over he noticed how they left these split bones +scattered upon the floor of the cave mingling with the sabre-shaped +teeth of the tiger, and this reminded him of the bones of the stag and +the tiger's tooth which he had found in Kent's Cavern in Devonshire only +a few days before. + +By this time the men had lain down to sleep, and in the darkness strange +cries were heard from the forest. The roar of the lion, mingled with the +howling of the wolves and the shrill laugh of the hyaenas, told that they +had come down to feed on the remains of the tiger. But none of these +animals ventured near the glowing fire at the mouth of the cavern, +behind which the men slept in security till the sun was high in the +heavens. Then all was astir again, for weapons had been broken in the +fight, and some of the men sitting on the ground outside the cave placed +one flint between their knees, and striking another sharply against it +drove off splinters, leaving a pointed end and cutting edge. They +spoiled many before they made one to their liking, and the entrance to +the cave was strewn with splintered fragments and spoilt flints, but at +last several useful stones were ready. Meanwhile another man, taking his +rude stone axe, set to work to hew branches from the trees to form +handles, while another, choosing a piece remaining of the body of the +stag, tore a sinew from the thigh, and threading it through the large +eye of the bone needle, stitched the tiger's skin roughly together into +a garment. + +"_This, then_," said the magician to himself, "_is how ancient man lived +in the summer-time, but how would he fare when winter came?_" As he +mused the scene gradually changed. The glaciers crept far lower down +the valleys, and the hills, and even the lower ground, lay thick in +snow. The hippopotamus had wandered away southward to warmer climes, as +animals now migrate over the continent of America in winter, and with +him had gone the lion, the southern elephant, and other summer visitors. +In their place large herds of reindeer and shaggy oxen had come down +from the north and were spread over the plains, scraping away the snow +with their feet to feed on the grass beneath. The mammoth, too, or hairy +elephant, of the same extinct species as those which have been found +frozen in solid ice under a sandbank in Siberia, had come down to feed, +accompanied by the woolly rhinoceros; and scattered over the hills were +the curious horned musk-sheep, which have long ago disappeared off the +face of the earth. Still, bitterly cold as it was, the hunter clad in +his wild-beast skin came out from time to time to chase the mammoth, the +reindeer, and the oxen for food, and cut wood in the forest to feed the +cavern fires. + +This time the magician's thoughts wandered down to the south-west of +France, where, on the banks of a river in that part now called the +Dordogne, a number of caves not far from each other formed the home of +savage man. Here he saw many new things, for the men used arrows of +deer-horn and of wood pointed with flint, and with these they shot the +birds, which were hovering near in hopes of finding food during the +bitter weather. By the side of the river a man was throwing a small dart +of deer-horn fastened to a cord of sinews, with which from time to time +he speared a large fish and drew it to the bank. + +[Illustration: Fig. 79. + +Mammoth engraved on ivory by Palaeolithic man.] + +But the most curious sight of all, among such a rude people, was a man +sitting by the glowing fire at the mouth of one of the caves scratching +a piece of reindeer horn with a pointed flint, while the children +gathered round him to watch his work. What was he doing? See! gradually +the rude scratches began to take shape, and two reindeer fighting +together could be recognised upon the horn handle. This he laid +carefully aside, and taking a piece of ivory, part of the tusk of a +mammoth, he worked away slowly and carefully till the children grew +tired of watching and went off to play behind the fire. Then the +magician, glancing over his shoulder, saw a true figure of the mammoth +scratched upon the ivory, his hairy skin, long mane, and up-curved tusks +distinguishing him from all elephants living now. "_Ah_," exclaimed the +magician aloud, "_that is the drawing on ivory found in the cave of La +Madeleine in Dordogne, proving that man existed ages ago, and even knew +how to draw figures, at a time when the mammoth, or hairy elephant, long +since extinct, was still living on the earth!_" + +With these words he started from his reverie, and knew that he had been +dreaming of Palaeolithic man who, with his tools of rough flints, had +lived in Europe so long ago that his date cannot be fixed by years, or +centuries, or even thousands of years. Only this is known, that, since +he lived, the mammoth, the sabre-toothed tiger, the cave-bear, the +woolly rhinoceros, the cave-hyaena, the musk-sheep, and many other +animals have died out from off the face of the earth; the hippopotamus +and the lion have left Europe and retired to Africa, and the sea has +flowed in where land once was, cutting off Great Britain and Ireland +from the continent. + +How long all these changes were in taking place no one knows. When the +magician drifted back again into his dream the land had long been +desolate, and the hyaenas, which had always taken possession of the caves +whenever the men deserted them for awhile, had now been undisturbed for +a long time, and had left on the floor of the cave gnawed skulls and +bones, and jaws of animals, more or less scored with the marks of their +teeth, and these had become buried in a thick layer of earth. The +magician knew that these teeth marks had been made by hyaenas, both +because living hyaenas leave exactly such marks on bones in the present +day, and because the hyaena bones alone were not gnawed, showing that no +animals preyed upon their flesh. He knew too that the hyaenas had been +there long after man had ceased to use the caves, because no flint +tools were found among the bones. But now the age of hyaenas, too, was +past and gone, and the caves had been left so long undisturbed that in +many of them the water dripping from the roof had left film after film +of carbonate of lime upon the floor, which as the centuries went by +became a layer of stalagmite many feet thick, sealing down the secrets +of the past. + + * * * * * + +The face of the country was now entirely changed. The glaciers were +gone, and so, too, were all the strange animals. True, the reindeer, the +wild ox, and even here and there the Irish elk, were still feeding in +the valleys; wolves and bears still made the country dangerous, and +beavers built their dams across the streams, which were now much smaller +than formerly, and flowed in deeper channels, carved out by water during +the interval; but the elephants, rhinoceroses, lions, and tigers were +gone never to return, and near the caves in which some of the people +lived, and the rude underground huts which formed the homes of others, +tame sheep and goats were lying with dogs to watch them. Also, though +the land was still covered with dense forests, yet here and there small +clearings had been made, where patches of corn and flax were growing. +Naked children still played about as before, but now they were moulding +cups of clay like those in which food was being cooked on the fire +outside the caves or huts. Some of the women, dressed partly in skins of +beasts, partly in rough woven linen, were spinning flax into thread, +using as a spinning-whorl a small round stone with a hole in the middle +tied to the end of the flax, as a weight to enable them to twirl it. +Others were grinding corn in the hollow of a large stone by rubbing +another stone within it. + +[Illustration: Fig. 80. + +Neolithic implements. + +1, Stone hatchet mounted in wood. 2, Jade celt, a polished stone weapon, +from Livermore in Suffolk, 1/4 size. 3, Spindle whorl, 1/2 size.] + +The men, while they still spent much time in hunting, had now other +duties in tending the sheep and goats, or looking after the hogs as they +turned up the ground in the forest for roots, or sowing and reaping +their crops. Yet still all the tools were made of stone, no longer rough +and merely chipped like the old stone weapons, but neatly cut and +polished. Stone axes with handles of deer-horn, stone spears and +javelins, stone arrowheads beautifully finished, sling-stones and +scrapers, were among their weapons and tools, and with them they made +many delicate implements of bone. On the broad lakes which here and +there broke the monotony of the forests, canoes, made of the trunks of +trees hollowed out by fire, were being paddled by one man, while +another threw out his fishing line armed with delicate bone-hooks; and +on the banks of the lakes, nets weighted with drilled stones tied on to +the meshes were dragged up full of fish. + +For these Neolithic men, or men of the New Stone Period, who used +polished stone weapons, were farmers and shepherds and fishermen. They +knew how to make rude pottery, and kept domestic animals. Moreover, they +either came from the east or exchanged goods by barter with tribes +living more to the eastward, now that canoes enabled them to cross the +sea; for many of their weapons were made of greenstone or jade, and of +other kinds of stone not to be found in Europe, and their sheep and +goats were animals of eastern origin. They understood how to unite to +protect their homes, for they made underground huts by digging down +several feet into the ground and roofing the hole over with wood coated +with clay; and often long passages underground united these huts, while +in many places on the hills, camps, made of ramparts of earth surrounded +by ditches, served as strongholds for the women and children and the +flocks and herds, when some neighbouring tribe attacked their +homesteads. + +Still, however, where caves were ready to hand they used them for +houses, and the same shelter which had been the home of the ancient +hunters, now resounded with the voices of the shepherds, who, treading +on the sealed floor, little dreamt that under their feet lay the remains +of a bygone age. + +[Illustration: Fig. 81. + +A burial in Neolithic times.] + +And now, as our dreamer watched this new race of men fashioning their +weapons, feeding their oxen, and hunting the wild stag, his attention +was arrested by a long train of people crossing a neighbouring plain, +weeping and wailing as they went. At the head of this procession, lying +on a stretcher made of tree-boughs, lay a dead chieftain, and as the +line moved on, men threw down their tools, and women their spinning, and +joined the throng. On they went to where two upright slabs of stone with +another laid across them formed the opening to a long mound or chamber. +Into this the bearers passed with lighted torches, and in a niche ready +prepared placed the dead chieftain in a sitting posture with the knees +drawn up, placing by his side his flint spear and polished axe, his +necklace of shells, and the bowl from which he had fed. Then followed +the funeral feast, when, with shouts and wailing, fires were lighted, +and animals slaughtered and cooked, while the chieftain was not +forgotten, but portions were left for his use, and then the earth was +piled up again around the mouth of the chamber, till it should be opened +at some future time to place another member of his family by his side, +or till in after ages the antiquary should rifle his resting-place to +study the mode of burial in the Neolithic or Polished Stone Age. + +Time passed on in the magician's dream, and little by little the caves +were entirely deserted as men learnt to build huts of wood and stone. +And as they advanced in knowledge they began to melt metals and pour +them into moulds, making bronze knives and hatchets, swords and spears; +and they fashioned brooches and bracelets of bronze and gold, though +they still also used their necklaces of shells and their polished stone +weapons. They began, too, to keep ducks and fowls, cows and horses; they +knew how to weave in looms, and to make cloaks and tunics; and when they +buried their dead it was no longer in a crouching position. They laid +them decently to rest, as if in sleep, in the barrows where they are +found to this day with bronze weapons by their side. + +Then as time went on they learnt to melt even hard iron, and to beat it +into swords and plough-shares, and they lived in well-built huts with +stone foundations. Their custom of burial, too, was again changed, and +they burnt their dead, placing the ashes in a funeral urn. + +[Illustration: Fig. 82. + +British relics. + +1, A coin of the age of Constantine. 2, Bronze weapon from a Suffolk +barrow. 3, Bronze bracelet from Liss in Hampshire.] + +By this time the Britons, as they were now called, had begun to gather +together in villages and towns, and the Romans ruled over them. Now when +men passed through the wild country they were often finely dressed in +cloth tunics, wearing arm rings of gold, some even driving in +war-chariots, carrying shields made of wickerwork covered with leather. +Still many of the country people who laboured in the field kept their +old clothing of beast skins; they grew their corn and stored it in +cavities of the rocks; they made basket-work boats covered with skin, in +which they ventured out to sea. So things went on for a long period till +at last a troubled time came, and the quiet valleys were disturbed by +wandering people who fled from the towns and took refuge in the +forests; for the Romans after three hundred and fifty years of rule had +gone back home to Italy, and a new and barbarous people called the +Jutes, Angles, and Saxons, came over the sea from Jutland and drove the +Britons from their homes. + +[Illustration: Fig. 83. + +Britons taking refuge in the Cave.] + +And so once more the caves became the abode of man, for the harassed +Britons brought what few things they could carry away from their houses +and hid themselves there from their enemies. How little they thought, as +they lay down to sleep on the cavern floor, that beneath them lay the +remains of two ages of men! They knew nothing of the woman who had +dropped her stone spindle-whorl into the fire, on which the food of +Neolithic man had been cooking in rough pots of clay; they never dug +down to the layer of gnawed bones, nor did they even in their dreams +picture the hyaena haunting his ancient den, for a hyaena was an animal +they had never seen. Still less would they have believed that at one +time, countless ages before, their island had been part of the +continent, and that men, living in the cave where they now lay, had cut +down trees with rough flints, and fought with such unknown animals as +the mammoth and the sabre-toothed tiger. + +But the magician saw it all passing before him, even as he also saw +these Britons carrying into the cave their brooches, bracelets, and +finger rings, their iron spears and bronze daggers, and all their little +household treasures which they had saved in their flight. And among +these, mingling in the heap, he recognised Roman coins bearing the +inscription of the Emperor Constantine, and he knew that it was by these +coins that he had, a few days before in Yorkshire, been able to fix the +date of the British occupation of a cave. + + * * * * * + +And with this his dream ended, and he found himself clutching firmly the +horn on which Palaeolithic man had engraved the figure of the reindeer. +He rose, and stretching himself crossed the sunny grass plot of the +quadrangle and entered his classroom. The boys wondered as he began his +lecture at the far-away look in his eyes. They did not know how he had +passed through a vision of countless ages; but that afternoon, for the +first time, they realised, as he unfolded scene after scene, the history +of "The Men of Ancient Days." + + + + +INDEX + + + Abbot's Way across Dartmoor, 196 + + Absorption of rays of sunlight, 129 + + Abyssinia, wild ass of, 203 + + _Actinozoa_, Cydippe allied to the, 190 + + Ages, lapse of between old and new stone age, 217 + + Alcor, or Jack, 158 + + Aldebaran, 149; + called so by the Arabs, 153; + colour of, 167 + + Algol the Variable, 162, 165 + + Almach, [Greek: g] Andromedae, 156; + a coloured double star, 167 + + America, extinction of original horse in, 207 + + Andromeda, the great nebula of, 162, 164; + double coloured star in, 167 + + Animal of the Sea-mat, 191; + number in one leaf, 193 + + Animal-trees and stony plants, 178 + + Animals, extinct, living with man, 211 + + Antares, a ruby-red star, 167 + + Antherozoids of mosses, 89 + + Apothecia of lichens, 83 + + Apennines, Lunar, figured, 19 + + Archimedes, a lunar crater, 10; + smooth centre of, 19 + + Arctic lands, lichens in, 82 + + Arcturus, colour of, 166 + + Aristarchus, a lunar crater, 10, 24; + streaks around, 17 + + Aristotle, a lunar crater, 10 + + Arrows, old stone, 215 + + Asia, horse of Central, 201 + + _Asinus taeniopus_, 203 + + _Aspergillus glaucus_, 61; + growth of, 63 + + Ass tribe, forms allied to the, 201 + + Ass, wild of Africa, 203 + + Atmosphere, absence of in the moon, 21 + + Australia, wild horses of, 207 + + + _Bacillaria Paradoxa_, a diatom, 185 + + Bacteria growing on wounds, 66 + + Baiae, hill thrown up on Bay of, 103 + + Ball, Sir R., on binary stars, 154 + + Beehive, triple star near the, 168 + + Beer, fermentation of, 65 + + Bellatrix, a star in Orion, 148 + + Berlin, ground beneath, formed of diatoms, 186 + + Bessel, on movements of Sirius, 169 + + Betelgeux, a star in Orion, 148 + + Binary star in Great Bear, 157, 158 + + Binary stars, 154, 166, 170 + + Bog-moss or Sphagnum, 93 + + Bog-mosses, distribution of, 94 + + Bombs, volcanic, 105 + + Booetis [Greek: e], a coloured double star, 167 + + Britons inhabiting caves, 224; + ornaments and customs of, 223 + + Britons of Dartmoor, 196 + + Bronze weapon and bracelet, 223 + + Bryum or thread moss, 77 + + Buckfast Abbey, monks of, 196 + + Bunt, a fungus, 64 + + Burial in Neolithic times, 221 + + Cassiopeia, the constellation, 162; + coloured double star in, 167 + + Castor, a binary star, 154 + + Camera, photographic, 47; + attached to the telescope, 121 + + Cancer [Greek: z], a triple coloured star, 168 + + Candle-flame, image of, formed by lens, 33 + + Canis Major, constellation of, 148 + + Capella, colour of the star, 153 + + Castor, light of compared with a near star, 158 + + Caterpillars destroyed by fungus, 66 + + Caucasus Mountains on the Moon, 18 + + Cave, the three periods of a, 225 + + Caves, Palaeolithic and Neolithic, 210; + Palaeolithic life in, 211; + hyaenas roamed in, 217; + Neolithic life in, 218; + Britons took refuge in, 224 + + Cells, fertile of mushroom, 69; + of moss-plant, 89 + + Celt, jade, from Suffolk, 219 + + Chambers, Mr., his drawing of [Greek: e] Lyrae, 166 + + Charles's Wain, 155; + part of Great Bear, 157; + stars of drifting, 159; + stars visible in waggon of, 160; + double coloured star in, 158, 167 + + _Chilomonas amygdalum_, a monad, 182 + + Ciliary muscle, action of the, 34 + + Clark, Alvan, on companion of Sirius, 169 + + Clockwork of telescope, 2 + + _Cocconema lanceolatum_, a diatom, 184 + + Coin of age of Constantine, 223 + + _Confervae_, growth of, 79 + + Commons, Mr., photographed Orion's nebula, 152 + + Constantine, coin of age of, 223 + + Constellations, maps of, 148, 156 + + Copernicus, a lunar crater, 10, 24; + figured, 17; + bright streaks around, 18 + + Copper-sulphate in lava, 108 + + _Corallina_, a stony seaweed, 175; + fruit of, 177; + appearance like _Sertularia_, 179 + + Cornea of the eye, 31 + + Corona, nature of the sun's, 123, 137 + + Cottam, Mr. A., his plate of coloured stars, 167 + + Crater, lava flowing from a, 98; + interior of Vesuvius, 100 + + Crater-plains, 19-21 + + Craters on the moon, 10, 13, 17, 19, 20; + of earth and moon compared, 16 + + Crystallites in volcanic glass, 109 + + Crystallisation, two periods of, in lava, 115 + + Crystals forming in artificial lavas, 114; + precious, 116 + + _Cydippe pileus_, a living jelly-ball, 187; + structure of, 188-190 + + Cygni [Greek: b], a coloured double star, 167 + + + Dartmoor, fairy rings on, 57, 58; + the Sundew on, 56; + granite figured, 112; + ponies, 195 + + De la Rue, his photograph of moon, 13 + + Devonshire ponies, black stripe on, 201 + + Diatom, a growing, 185 + + _Diatoma hyalina_, 184 + + Diatoms, magnified fossil, 39; + living marine, 184 + + Didymium, giving a broken spectrum, 126 + + Dordogne, caves of the, 210, 215 + + Draper, Prof., photographed Orion's nebula, 152 + + _Drosera rotundifolia_ on Dartmoor, 56 + + Dschiggetai, horse-ass of Tibet, 200 + + Dsungarian desert, wild horse of the, 203 + + Dykes, nature of volcanic, 111 + + + Earth, path of the moon round the, 8; + magnetic storm on, caused by sun, 14; + reservoirs of melted matter in the, 101 + + Earthquakes accompanying volcanic outbursts, 102 + + Eclipse of sun, red jets and corona seen during, 125 + + Eclipse, total, of the moon, 23; + lurid light during, 25 + + Eclipses, how caused, 7 + + Elephant, hairy, engraved on ivory, 216 + + _Empusa muscae_, 66 + + Engis and Engihoul caves, 210 + + England, ancient caves in, 210; + in Palaeolithic times, 211 + + Eocene, toed horses of the, 205 + + _Eohippus_, or horse of the dawn, 205 + + _Equus hemionus_, the horse-ass, 202 + + Eratosthenes, a lunar crater, 10 + + Erbia, giving a broken spectrum, 126 + + Ergot, a fungus, 61 + + Eruptions of Vesuvius, 97, 100, 104 + + Eudoxus, a lunar crater, 10 + + Experiments, necessity for accurate, 54 + + Eye, structure of the, 29-32; + mode of seeing with the, 32; + short-sighted, 29, 35; + distances spanned by the naked, 40 + + + Faculae on the sun's face, 122, 140 + + Fairy rings, 55; + mentioned in _Merry Wives of Windsor_, 57; + growth of, 71-73 + + Ferments caused by fungi, 60, 64 + + Fishing in ancient times, 215, 220 + + _Fistulina hepatica_, a fungus, 71 + + Flint skeletons of plants, 185 + + Flustra or sea-mat, 187; + structure of, 191-193 + + Fly, fungus killing a, 66 + + Focal images, 33; + distances, 44 + + Fouque, M., artificial lava made by, 112 + + Fructification of mushrooms, 69; + of lichens, 83; + of mosses, 91; + of seaweeds, 177 + + _Funaria hygrometrica_, urn of the, 89, 91; + has no urn lid, 92 + + Fungi, nature of, 59; + different kinds of, 60; + attacking insects, 66; + growing on wounds, 66; + the use of, 74 + + Fungus and green cells in lichen, 81 + + + Gardener, advice of the old, 118 + + Gas, spectrum of a, 126 + + Gases revealed by spectroscope, 52 + + Gemini, the constellation, 154 + + Geminorum, [Greek: d], a double coloured star, 167 + + Gills of mushroom, 69 + + _Gomphonema marinum_, 184 + + Gooseberry, fermentation in a, 64 + + Gory dew, _Palmella cruenta_, 79 + + Graham's island thrown up, 102 + + Granular appearance of sun's face, 123 + + Grape fungus, 65 + + Great Bear, the constellation, 157; + binary star in, 158; + coloured double star in, 158, 168 + + Greenstone, Neolithic weapons of, 220 + + Guards, the, in the Little Bear, 162 + + + Hartz Mountains, caves of the, 210 + + Hatchet, a Neolithic stone, 219 + + Hebrides, volcanic islands of, 111 + + Henri, MM., photograph of moon's face by, 19 + + Herculaneum, buried, 98, 104 + + Herculis [Greek: a], a coloured double star, 168 + + Hermitage, lava stream flowing behind the, 97, 99 + + Herschel's drawing of Copernicus, 17 + + Huggins, Dr., on shape of prominences, 135; + on spectra of nebulae, 151; + on cause of colour in stars, 168 + + Himalayas, single-celled plants in the, 79 + + Horse, wild, of the Pampas, 198; + of Tartary, 199; + of Kirghiz steppes, 200; + Przevalsky's, 202; + early history of toed, 204; + structure of foot and hoof of, 205; + skeleton of, 206; + origin and migration of early, 207 + + Hungary, ancient caves of, 210 + + Huyghens, the highest peak in Lunar Apennines, 19 + + + Image formed at focus of lens, 33; + of sky in telescope, 49 + + Implements, old stone, 213; + new stone, 219 + + Imps of plant-life, 59 + + India, low plants in springs of, 79; + solar eclipse seen in, 124; + wild ass of, 203 + + Infusorial earth, 186 + + Infusorians in a seaside pool, 183 + + Inhabitants of a seaside pool, 172-174 + + Iris of the eye, 30 + + Iron pyrites in lava, 108 + + Iron slag, lava compared to, 105 + + Islands, volcanic thrown up, 102 + + + Jack by the second horse, 157 + + Jade, Neolithic weapons of, 220 + + Jannsen, Prof., on sun prominences, 131 + + Judd, Mr., on volcano of Mull, 111 + + Jutes and Angles invading Britain, 224 + + + Kant on nebular hypothesis, 152 + + Kent's Cavern, rough stone implement from, 213 + + Kepler, a lunar crater, 10; + streaks around, 17 + + Kertag, or wild horse, 202 + + Kew, sun-storm registered at, 143 + + Kiang or Kulan, 200 + + Kirchhoff, Prof., on sunlight, 128 + + Kulan or Kiang, 200 + + + Labrador felspar artificially made, 113 + + Langley, Prof., sun-spot drawn by, 141 + + Laplace, nebular hypothesis of, 152 + + Lava, aspect of flowing, 99; + reservoirs of molten, 101; + nature of, 107; + artificially made, 113; + two periods of crystallisation in, 115 + + Lava-stream, history of a, 100; + section of a, 108; + rapid cooling of surface, 108 + + Laver or sea-lettuce, structure of, 176 + + Leo, the constellation, 155 + + Leucotephrite artificially made, 113 + + Lens, natural, of the eye, 31; + simple magnifying, 35 + + Levy, M., artificial lava made by, 112 + + Lichens, specimens of from life, 77; + the life-history of, 80-84; + sections of, 81; + distribution of 82, 95; + fructification of, 83; + causes of success of, 94 + + Lick telescope, magnifying power of, 46 + + Light, lurid, on moon during eclipse, 24; + sifted by spectroscope, 126 + + Light-granules on sun's face, 123; + supposed explanation of, 141 + + Lime-tree, fungi on the, 64 + + Liss, bronze bracelet from, 223 + + Little Bear, pole-star and guards in the, 162 + + Lockyer, Mr., on sun-prominences, 131, 136 + + Lunar Apennines figured, 19 + + Lyrae [Greek: epsilon], a double-binary star, 166 + + + Machairodus, tooth of, 213 + + Madeleine, La, carvings from cave of, 216 + + Magic glasses and how to use them, 27; + what can be done by, 28, 53 + + Magician's chamber, 1; + his pupils, 4; + spells, 28; + his dream of ancient days, 209 + + Magnetic connection of sun and earth, 142 + + Magnifying-glass, action of a, 35 + + Mammoth engraved on ivory, 216 + + Maps of constellations, 148, 156 + + _Marasmius oreastes_, fairy-ring mushroom, 55, 72 + + _Mazeppa_, quotation from Byron's, 201 + + Men of older stone age, 212; + of Neolithic age, 218 + + _Mesohippus_, a toed horse, 205 + + Microliths in volcanic glass, 109, 110, 113, 115; + formed in artificial lava, 113 + + Microscope, 3; + action of the, 36-38 + + Mildews are fungi, 60 + + Milky Way, 149; + Cassiopeia in the, 163 + + Minerals crystallising in lava, 108 + + Mines, increase of temperature in, 101 + + Miohippus, or lesser toed horse, 206 + + Mizar, a double-coloured star in the Great Bear, 158, 168 + + Monads, size and activity of, 183 + + Monks, ancient, of Dartmoor, 196 + + Monte Nuovo thrown up in 1538, 103 + + Moon, phases of the, 6; + course in the heavens, 8; + map of the, 10; + craters of the, 10, 13, 17, 19, 20; + face of full, 11; + a worn-out planet, 21; + no atmosphere in the, 21; + diagram of eclipse of, 23; + lurid light on during eclipse, 24 + + Moss-leaf magnified, 87 + + Moss, life-history of a, 84, 92; + a stem of feathery, 85; + protonema of a, 86; + modes of new growth of a, 88; + fructification of a, 89; + urns of a, 89, 91 + + Mosses, different kinds of, 77; + advantages and distribution of, 94 + + Moulds are fungi, 60; + how they grow, 63 + + Mountains of the moon, 19; + formation of, 21 + + _Mucor Mucedo_, figured, 61; + growth of, 63 + + Mull, volcanic dykes in the island of, 111 + + Mushroom, early stages and spawn of, 67; + mycelium of, 67; + later stages of, 68; + section of gills of, 69; + spores of, 70; + fairy or Scotch bonnet, 72 + + Mycelium of mould, 63; + of mushroom, 67; + of fairy rings, 72 + + + Naples, volcanic eruption seen at, 96; + Monte Nuovo thrown up near, 103 + + Nasmyth on bright lunar streaks, 16 + + Nebula of Orion, 149; + spectrum of, 151; + photographs of, 152; + of Pleiades, 153; + of Andromeda, 163-164 + + Needle, bone, from a cave, 212 + + Neolithic implements, 219; + industries and habits, 218-220; + burials, 221 + + Neptune, invisible to naked eye, 35 + + Neison, Mr., his drawing of Plato, 20 + + _Nostoc_, growing on stones, 79 + + + Oak, fungi on the, 64 + + Observatory, the Magician's, 2; + astronomical on Vesuvius, 97; + cascade of lava behind the, 99 + + Obsidian, or volcanic glass, 109 + + Occultation of a star, 22, 25 + + Onager, or wild ass of Asia, 203 + + Optic nerve of eye, 34 + + Orion, constellation of, 147, 149; + great nebula of, 149; + photographs of Nebula of, 152; + coloured double stars in, 168 + + Orionis [Greek: th], or Trapezium, 150 + + Ornaments of ancient Britons, 222 + + Orohippus, a toed horse, 205 + + _Oscillariae_, growth of, 79 + + + Palaeolithic man, 212; + relics, 213; + life, 214, 216 + + Pampas, wild horses of the, 198 + + _Penicillium glaucum_, figured, 61; + growth of, 63 + + Penumbra of an eclipse, 23; + of sun-spots, 140 + + Perithecia of lichens, 84 + + Petavius, a lunar crater, 10 + + Photographic camera, 3, 47; + attached to telescope, 121 + + Photographs of the moon, 13, 19; + of galloping horse, 48; + of the stars, 49, 161; + of the sun, 121 + + Photosphere of the sun, 123 + + Philadelphia, electric shocks at during sun-storm, 143 + + Pixies of plant life, 59 + + Plains of the moon, 10; + nature of the, 12 + + Plants, colourless, single-celled, 65; + single-celled green, 78; + two kinds of in lichens, 80; + with flint skeletons, 185 + + Plato, a lunar crater, 10, 24; + figured, 20 + + Pleiades, the, 153; + nebulae in, 153 + + _Pleurococcus_, a single-celled plant, 78 + + Plough, the, or Charles's Wain, 157 + + Pointers, in Charles's Wain, 161 + + Pole-star, the, 161; + a yellow sun, 166 + + Pollux, a yellow sun, 166 + + _Polysiphonia_, a red seaweed, 175; + fruit of, 177 + + _Polytrichum commune_, a hair moss, 88; + its urns protected by a lid, 91 + + Pool, inhabitants of a seaside, 172-74 + + Precious stones, formation of, 116 + + Proctor, his star atlas, 146; + on drifting of Charles's Wain, 159 + + Prominence-spectrum and sun-spectrum compared, 134 + + Prominences, red, of the sun, 125; + seen in full daylight, 131-133; + shape of, 135 + + _Protococcus nivalis_, 79 + + Protonema of a moss, 86 + + Przevalsky's wild horse, 202 + + Ptolemy, a lunar crater, 10 + + Puffballs, 67, 70; + use of in nature, 73 + + Pupil of the eye, 30 + + Puzzuoli, eruption near, 1538, 103 + + + Quaggas, herds of, 203 + + + Rain-band in the solar spectrum, 130 + + Rain-shower during volcanic eruption, 107 + + Readings in the sky, 53, 127, 151, 168 + + Red snow, a single-celled plant, 79 + + Regulus, the star, 155, 166 + + Reindeer, carving on horn of, 216 + + Reservoirs of molten rock underground, 101 + + Resina, ascent of Vesuvius from, 98 + + Retina of the eye, 31; + image of object on the, 33 + + Richmond, Virginia, infusorial earth of, 186 + + Rigel, a star in Orion, 149; + a coloured double star, 168 + + Rings, growth of fairy, 73 + + Roberts, Mr. I., his photograph of Orion's nebula, 152; + and of nebula of the Pleiades, 153; + and of nebula of Andromeda, 164 + + Rosse, Lord, his telescope, 46; + on Orion's nebula, 150; + stars visible in his telescope, 160 + + Rue, De la, his photograph of the moon, 13 + + Rust on plants, 61 + + + Sabrina island formed, 102 + + Saturn, distance of, 40 + + Saxons, invasion of the, 224 + + Schwabe, Herr, on sun-spots cycle, 137 + + Scoriae of volcanoes, 108 + + "Scotch bonnet" mushroom, 72 + + Sea-mat, _see_ Flustra + + "Seas" lunar, so-called, 10 + + Seaweeds, a group of, 175; + fruits of, 177 + + Secchi, Father, on depth of a sun-spot, 139 + + Selwyn, Mr., photograph of sun by, 122 + + Senses alone tell us of outer world, 29 + + _Sertularia tenella_, structure of, 180; + _cupressina_, 181 + + Sertularian and coralline, resemblance of, 179 + + Shakespeare on fairy rings, 57 + + Shipley, Mr., saw volcanic island formed, 103 + + Sight, far and near, 35 + + Silkworm destroyed by fungi, 66 + + Sirius, 146; + a bluish white sun, 166; + irregularities of caused by a companion, 169 + + Skeleton of the horse, 206 + + Skin diseases caused by fungi, 61, 66 + + Sky, light readings in the, 53, 127, 151, 168 + + Smut, a fungus, 61 + + Sodium lime in the spectrum, 128 + + Somma, part of ancient Vesuvius, 97, 104 + + Spawn of mushroom, 67 + + Spectra, plate of coloured, 127 + + Spectroscope, 3; + Kirchhoff's, 51; + gases revealed by the, 52; + direct vision, 127; + sifting light, 126; + attached to telescope, 132 + + Spectrum of sunlight, 127, 130 + + Sphacelaria, a brown-green seaweed, 175; + fruit of, 177 + + Sphagnum or bog moss, 77, 93; + structure of leaves of, 93 + + Spindle-whorl from Neolithic caves, 219 + + Spore-cases of mosses, 89, 91, 93 + + Spores of moulds, 63; + of mushroom, 70; + of lichens, 83; + of mosses, 91 + + Star, occultation of, by the moon, 24; + a double-binary, 166; + a dark, travelling round Sirius, 169 + + Star-cluster in Perseus, 162 + + Star-depths, 160, 171 + + Stars, light from the, 40, 42; + visible in the country, 145; + apparent motion of the, 146; + maps of, 148, 156; + of milky way, 149; + binary, 154; + real motion of, 159; + drifting, 159; + number of known and estimated, 161; + colours of, 166; + double coloured, 167; + cause of colour in, 168; + are they centres of solar systems? 170 + + Statur or wild horse, 202 + + Streaks, bright, on the moon, 14-17 + + Suffolk, bronze weapon from barrow in, 223 + + Sun, path of the moon round the, 8; + one of the stars, 119; + how to look at the, 119; + face of, thrown on a screen, 120; + photograph of the, 122; + prominences, corona, and faculae of, 122-125; + mottling of face of, 123; + total eclipse of, 124; + zodiacal line round, 125; + dark lines in spectrum of, 128; + reversing layer of, 131; + metals in the, 131; + sudden outburst in the, 142; + magnetic connection with the earth, 143; + a yellow star, 166 + + Sun's rays touching moon during eclipse, 24 + + Sun-spots, cycle of, 137; + proving sun's rotation, 138; + nature of, 139; + quiet and unquiet, 140; + formation of, 142 + + Sundew on Dartmoor, 56 + + + Tarpan, a wild horse, 199 + + Tartary, wild horses of, 199 + + Tavistock Abbey, monks of, 196 + + Telescope, clock-work, adjusting a, 2; + an astronomical, 41; + magnifying power of the, 43-46; + giant, 46; + terrestrial, 47; + what can be seen in a small, 46; + how the sun is photographed in the, 122; + how the spectroscope is worked with the, 132 + + Teneriffe, peak of compared to lunar craters, 15 + + Tennant, Major, drawing of eclipsed sun by, 123 + + Temperature, underground, 101 + + _Thuricolla follicula_, a transparent infusorian, 182 + + Tiger, sabre-toothed, 211, 213 + + _Tilletia caria_ or bunt, 64 + + Toadstools, 67, 70; + use of in nature, 73 + + Tools, of ancient stone period, 214, 215 + + Tooth of machairodus, 213 + + Torquay, the Magician's pool near, 172 + + Tors of Dartmoor, 197 + + Trapezium of Orion, 150 + + _Tremella mesenterica_ fungus, 71 + + Tripoli formed of diatoms, 35 + + Tundras, lichens and mosses of the, 82, 95 + + Tycho, a lunar crater, 10; + description of, 13; + bright streaks of, 14 + + + _Ulva_, a green seaweed, 175; + a section magnified, 176 + + Umbra of an eclipse, 23 + + Urns of mosses, 89, 91 + + _Ustilago carbo_, or smut, 64 + + Variable stars, 165 + + Vega, a bluish-white sun, 166; + double-binary star near, 165 + + Veil of mushroom, 68 + + Vesuvian lavas imitated, 113 + + Vesuvius, eruption of 1868 described, 97, 99, 104; + dormant, 103; + eruption of in A.D. 79, 104 + + Volcanic craters of earth and moon compared, 16; + eruptions in the moon, 21; + glass under the microscope, 109, 110, 115 + + Volcano, diagram of an active, 105 + + Volcanoes, the cause of discussed, 101, 102; + ancient, laid bare, 111 + + + Washington, electric shocks at during sun-storm, 143 + + Winter in Palaeolithic times, 215 + + Wood, winter growth in a, 76 + + "World without End," 115 + + + Yeast, growth of, 65 + + Yorkshire, Roman coins in caves of, 225 + + + Zebra, herds of, 203 + + Zodiacal light, 125 + + +THE END + + + * * * * * + + + + +D. APPLETON & CO.'S PUBLICATIONS. + + + _THE FAIRYLAND OF SCIENCE._ By ARABELLA B. BUCKLEY. With 74 + Illustrations. Cloth, gilt, $1.50. + +"Deserves to take a permanent place in the literature of +youth."--_London Times._ + +"So interesting that, having once opened the book, we do not know how to +leave off reading."--_Saturday Review._ + + + _LIFE AND HER CHILDREN: Glimpses of Animal Life from the Amoeba + to the Insects._ By ARABELLA B. BUCKLEY. With over 100 + Illustrations. Cloth, gilt, $1.50. + +"The work forms a charming introduction to the study of zoology--the +science of living things--which, we trust, will find its way into many +hands."--_Nature._ + + + _WINNERS IN LIFE'S RACE; or, the Great Backboned Family._ By + ARABELLA B. BUCKLEY. With numerous Illustrations. Cloth, gilt, + $1.50. + +"We can conceive no better gift-book than this volume. Miss Buckley has +spared no pains to incorporate in her book the latest results of +scientific research. 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